Pooh and his friends along with Pooh's old princess allies: Belle, Jasmine, Odette, Ariel, Aurora, and Tiana meet Mia Thermopolis (Anne Hathaway) a fifteen-year-old tenth grade private school student who lives with her mother Helen Thermopolis (Caroline Goodall) and her cat, Fat Louie, in a San Francisco firehouse. Her father, Philippe Renaldi (who was divorced but in touch with her) died two months earlier in a car crash. Although Mia is an average student, she is very unpopular, but has three good friends: Lilly Moscovitz (Heather Matarazzo), Lilly's brother Michael Moscovitz (Robert Schwartzman) and of course, Tiana.
Shortly before Mia's sixteenth birthday, she learns from her mother that her paternal grandmother is visiting from Genovia, a country in Europe. At first Mia does not want to see her, but agrees later. The next day, Mia meets her grandmother, Clarisse Renaldi (Julie Andrews), at the Genovian consulate for the first time, who explains that the reason she wanted to see her was because of a "life-changing" problem. She learns that her father was the crown prince of Genovia and she is the next crown princess of Genovia and the only heir to the Genovian throne because of her father's death. She was shocked to learn that she is a princess.
Pooh, his companions, Mia's mother and grandmother convince her to attend "princess lessons" in preparation for her introduction to the Genovian government, under supervision from her new bodyguard, the head of Genovian security, Joseph "Joe" (Héctor Elizondo). To look more presentable to the Genovian government, Mia receives a makeover from Italian hairdresser Paolo (Larry Miller).
A couple of days later, the San Francisco Chronicle learns that Mia is the Genovian heir after Paolo tells the media so everybody will know that he is the one that made Princess Mia look like a princess. Although unimpressed, Clarisse ignores the situation and prepares for the State Dinner, which Mia attends and is publicly humiliated. The day after the State Dinner, Mia, Pooh and the group agree to appear on Lilly's public-access television program Shut Up and Listen and to watch Michael's band perform at a venue that Saturday night. Mia is almost 16 so she is almost able to drive a car, (her "baby", a Ford Mustang.) She takes a test drive with her grandmother and takes her to the arcade. Mia asks her grandmother if her father wanted to be prince, to which she replies yes, but goes onto say that he fell in love with Mia's mother, but realised his love for his country was greater. When they are driving back, Mia's grandmother is in the front seat trying to give Mia some instruction on how to keep going. All goes well until Mia gets scared on a very steep hill, and this causes her to crash into a trolley load of people. A local policeman is called to the scene and is named to the fictional Genovian Order of the Rose for being an exceptional San Francisco citizen (along with the trolley master). This saves Mia from a ticket.
Josh Bryant, a cute boy whom Mia crushed on long before her princess makeover, asks Mia to go with him to the Baker Beach Bash, the school's annual beach party, and she excitedly agrees. She remembers to tell Michael that she will watch his band the following Saturday night, but forgets to tell Lilly of the change, causing Pooh and the gang to worry. The beach party goes well at first, but spirals out of control when the media learn of Mia's presence. Josh publicly embarrasses her by kissing her in front of photographers (much to Tigger's disgust). Right after, Lana and two of the most popular girls at school pretend to be on her side and give her clothes, although while she changes in a small tent, they let photographers wait right outside and then knock the tent over, revealing her with only her towel on. With Pooh and his friends left in shock, this causes a media frenzy and displeases Clarisse. Clarisse then gets a wake-up call from Joe, telling her that she has to remember that although Mia is a princess, and the heir to her throne, Mia is still her granddaughter. To reconstruct her friendships with Lilly and Michael, Mia invites them to the Genovian Independence Day Ball, where she must reveal whether or not she wants to accept her duties as a princess. Originally intent on running away to Colorado because she wants to avoid renouncing her throne with a speech (as she is terrible at public speaking), Mia finds a sixteenth birthday gift and letter from her father, written before his death. After reading the letter, she changes her mind and makes her way to the ball, as it begins raining. Her car's roof will not go up though, so she is stuck driving in the rain and her car breaks down when she attempts to go up the incredibly steep hill. Joe finds her drenched halfway to the event. Upon arrival, Mia makes a speech announcing her acceptance to the Genovian throne. Michael then takes her outside where they share their first kiss. While Pooh, Piglet, Tigger, Rabbit, Eeyore and Jiminy Cricket dance with the princesses, Clarisse and Joe also walk out of the Genovian consulate holding hands, showing sparks of a relationship. The last scene shows Mia on the plane to Genovia with her grandmother and her mother, writing in her diary. She explains that she is moving there, and Lily and Michael will visit for the summer holiday. When Mia finishes writing in her diary, she looks down to the ground from plane's window at the palace of Genovia.
- Belle, Princess Jasmine, Princess Odette, Ariel, Princess Aurora and Princess Tiana guest starred in this film.
- The Winnie the Pooh films, The Jungle Book, Pinocchio, The Lion King, Beauty and the Beast, Aladdin, The Little Mermaid, Sleeping Beauty, The Princess and the Frog, and The Princess Diaries were all made by Disney.
- Simba, Nala, Timon, Pumbaa, Genie, and Yogi Bear were originally planned to guest star in this film, until DisneyDaniel93 decided to cut them out of the film, because they weren't right for the movie. So Belle, Princess Jasmine, Princess Odette, Ariel, Princess Aurora, and Princess Tiana ended up being the only guest stars in this film, due to this film being a princess film, and Simba, Nala, Timon, and Pumbaa ended up guest starring in Thomas' Adventures of The Princess Diaries instead.
- This is an NTSC film with NTSC bits from Winnie the Pooh and a Day for Eeyore, The Tigger Movie, Winnie the Pooh: A Very Merry Pooh Year, Pooh's Heffalump Movie, Winnie the Pooh, The Jungle Book 2, Mickey's Christmas Carol, The Lion King films, Beauty and the Beast, the Aladdin films, The Little Mermaid films, Sleeping Beauty, and The Princess and the Frog and PAL bits from The Many Adventures of Winnie the Pooh, Pooh's Grand Adventure: The Search for Christopher Robin, Piglet's Big Movie, Pooh's Heffalump Halloween Movie, The Jungle Book, Pinocchio, Fun and Fancy Free, Belle's Magical World, Disney Princess Enchanted Tales: Follow Your Dreams, and The Swan Princess films.
- This is the first Pooh's Adventures crossover not to have The New Adventures of Winnie the Pooh intro (not even with clips from the original movie) since Pooh's Adventures of The Secret of NIMH. This is presumably because neither Josh Bryant nor Lana Thomas serves as the main villain; instead, the antagonist is really a situation Mia gets in, such as on the way to the Genovian ball when her car breaks down.
- Mia Thermopolis is revealed to be an old friend of Tiana.
- This film actually takes place after Bloom Meets The Princess and the Frog, which explains Princess Jasmine and Princess Odette already knowing Princess Tiana.
- This place takes after Littlefoot's Adventures of Sleeping Beauty, which explains The Vultures, Jiminy Cricket, and Zazu already knowing Princess Aurora.
- The Vultures, Jiminy Cricket, and Zazu will see Princess Jasmine again in Winnie the Pooh and The Return of Jafar.
- Due to being the first Winnie the Pooh crossover with Princess Odette since the death of her original voice actress, Michelle Nicastro (which happened on November 4, 2010), this was dedicated to her memory.
- Princess Odette is the only Non-Disney Princess to guest star in this film.
- The storyline continues in Pooh's Adventures of The Princess Diaries 2: Royal Engagement.
- This film is also inspired by the Disney Princess franchise.
- The clips of the Hundred Acre Crew dancing with the princesses were made by Startanica.
- Pooh's Adventures of The Princess Diaries Part 1: https://drive.google.com/file/d/0B35Ri2vUrFXpbGVPLTduYURCSGM/view
- Pooh's Adventures of The Princess Diaries Part 2: https://drive.google.com/file/d/0B35Ri2vUrFXpekp0RGl1V2djMmM/view
- Pooh's Adventures of The Princess Diaries Part 3: https://drive.google.com/file/d/0B35Ri2vUrFXpVnFPRmhwUGJZaWs/view
- Pooh's Adventures of The Princess Diaries Part 4: https://drive.google.com/file/d/0B35Ri2vUrFXpX3dtc2owTFF1Q0U/view
- Pooh's Adventures of The Princess Diaries Part 5: https://drive.google.com/file/d/0B35Ri2vUrFXpNTdTYWJKS2NnUG8/view
- Pooh's Adventures of The Princess Diaries Part 6: https://drive.google.com/file/d/0B35Ri2vUrFXpNVRqNzNGMXJNSDA/view
- Pooh's Adventures of The Princess Diaries Part 7: https://drive.google.com/file/d/0B35Ri2vUrFXpUUVudnZEblNyNTA/view
- Pooh's Adventures of The Princess Diaries Part 8: https://drive.google.com/file/d/0B35Ri2vUrFXpMy1mVzlCaUNXeTg/view
- Pooh's Adventures of The Princess Diaries Part 9/Credits: https://drive.google.com/file/d/0B35Ri2vUrFXpOEEyTklhOU85OVk/view