The film opens with a traditionally animated sequence featuring Fat Albert performing the original series' theme song "Gonna Have a Good Time".
In real life, Doris Robertson is a depressed teenager still recovering from the death of her grandfather, and she is ignoring her foster sister Lauri's efforts to bring her a social life. Upon learning that her parents will be away for a two-day business trip to the Poconos, Doris sadly lets a tear hit her TV remote, as Fat Albert and the Cosby Kids is on. The tear opens up a portal between the cartoon world and the real world and Fat Albert jumps out of the TV, knowing she has a problem. Then, Rudy, Dumb Donald, Mushmouth, Bucky, and Old Weird Harold jump out as well; Bill tells Russell to stay put and cover for them. Doris insists she is fine, but the gang knows otherwise and the show ends and they have to wait until the next day's show to come back. They follow Doris to school and are amazed by the new technology like pop cans, cell phones, and laptops.
Albert notices Lauri and falls in love with her. Reggie, an annoying schoolmate with an obsessive crush on Lauri, challenges Albert to a track race that Albert wins. In another attempt to help Doris, the gang persuades some cheerleaders to invite them all to an outdoor party. With some reluctance, Doris agrees to attend then went to a shopping mall. While at the party, Lauri dances with Albert. Reggie desperately attempts to make her jealous by dancing with Doris. When Lauri does not notice him, he tries to kiss Doris. Doris is offended and causes a scene. Albert warns the boy to stay away from Doris. The next day, Doris goes to school, but asks the gang to go to the park instead of following her. Harold, normally clumsy, joins in a basketball game and is able to play perfectly. Mushmouth, who cannot talk normally, is taught how to speak by a little girl. Donald goes to the library and is able to read and remove his pink face-covering hat.
When Doris takes them home, only three of the gang members, Bucky, Harold and Donald (whose eyes float in the TV without the hat on) jump into the TV, Breaking News interrupts the show before the other four can enter. Albert and Bill have an argument in private about going back. The gang takes Doris and Lauri to a fair on a junk-made car, Rudy; meanwhile, has fallen in love with Doris and ask her if she would go out with him if he was a real person and she said yes. Searching for guidance, Fat Albert literally meets his maker, Bill Cosby and tells him of the dilemma. Mr. Cosby tells him that his character is based on Doris' grandfather Albert Robertson which explains Doris' confusion over why Fat Albert seems so familiar to her. Mr. Cosby warns Fat Albert that he has to return to the cartoon world, or he will turn into celluloid dust (as indicated by the faded color of their clothes). Devastated, Albert tries to tell Lauri that he has to leave, but she thinks that he is just being insensitive. The next day, Rudy, Bill, and Mushmouth jump back into the TV (with Mushmouth starting to speak unclear again). Albert waits and go to the track meet, where Doris and Lauri are competing, encourages Doris to a victory. Reggie, who witnessed that the gang is from the TV, attempts to threaten Albert, but he pushes him aside. Albert rushes to the girls' home on a borrowed skateboard. He says goodbye to Doris and Lauri (who now believes that Albert is from the TV) and jumps back into the TV.
Sometime later, Mr. Cosby and his friends (who were in his routines, then were characters in the show) stand in front of their old friend Albert Robertson's grave. As the camera pans on each of the men, images of their counterparts are seen. Doris watches them. The old men race away; they are still kids at heart, the same kids from the TV show that they helped Bill Cosby inspire.
Before the end credits start, Fat Albert is trying to leap out of the movie screen, points out that people in the audience need help and he even tells someone in the back of the theater that he/she needs to come back and finish watching the credits. The boys pull Albert back inside and the end credits resume, beginning with the blend of both the animated characters' voices and the live-action characters singing the Fat Albert Theme Song.Kenan Thompson as "Fat" Albert Robertson
Kyla Pratt as Doris Robertson
Bill Cosby as Himself
Dania Ramirez as Lauri Robertson
Shedrack Anderson III as Rudy
Keith Robinson Bill
Marques Houston as Dumb Donald
Jermaine Williams as Mushmouth
Aaron Frazier as Harold Williams
Alphonso McAuley as Bucky
Omarion as Reggie
J. Mack Slaughter, Jr. as Arthur
Alice Greczyn as Becky
Rick Overton as Coach Gillespie
Keri Lynn Pratt as Heather
Dylan Cash as Emmitt
Aaron Carter as Darren (credited as "Teen")
Fonzworth Bentley as Salesman (as Derek "Mr. Bentley" Watkins)
Jeff Garlin as Jerry (uncredited)
Joel Madden as Classmate with Mohawk (uncredited)
Mase as Himself (archive footage)
Nick Zano as Cell phone salesman
Denise Richards as Saleswoman (appears in theatrical trailer, scenes deleted from the final cut)
Jeremy Suarez as Russell Cosby
Earl Billings as Mr. Mudfoot
Raven-Symoné as Danielle
Catero Colbert as Lead Teen
Charles Duckworth as Teen #1
Benjamin Diskin as Teen #2
Josh Uhler as Teen #3
Kevin Hart as Teen #4
Bill Ratner as Announcer
The filming locations were in Philadelphia, Los Angeles, and Valencia, Santa Clarita, California.
Fat Albert was released on VHS and DVD on March 22, 2005. There has yet to be a Blu-ray release of the film.
On Rotten Tomatoes, the film received a rating 25%, based on 89 reviews, with the consensus reading, "A bland but good-natured adaptation of the cartoon show." On Metacritic, the film holds a score of 39 out of 100, based on 26 critics, indicating "generally unfavorable reviews".
The film grossed $48.6 million worldwide, against a $45 million budget.