The film is noted for being the last film project to actually be approved by Walt Disney himself, as he died in late 1966, before the film was released. He had, however, been working in the story development for The Rescuers (1977) as early as 1962. The Aristocats gained positive reviews on first release and was a box office success.
In Paris in 1910, mother cat Duchess and her three kittens, Marie, Berlioz, and Toulouse, live with retired opera diva Madame Adelaide Bonfamille, and her English butler, Edgar. While preparing her will with lawyer Georges Hautecourt, Madame declares her fortune to be left to her cats until their deaths, and thereafter to Edgar. Edgar hears this through a speaking tube, and plots to eliminate the cats. Therefore, he sedates the cats by sleeping pills in their food, and enters the countryside to abandon them. There, he is ambushed by two hounds, named Napoleon and Lafayette, and the cats are stranded in the countryside, while Madame Adelaide, Roquefort the mouse, and Frou-Frou the horse discover their absence. In the morning, Duchess meets an alley cat named Thomas O'Malley, who offers to guide her and the kittens to Paris. The group briefly hitchhike in a milk cart before being chased off by the driver. Later, while crossing a railroad trestle, the cats narrowly avoid an oncoming train, but Marie falls into a river and is saved by O'Malley; himself rescued by two English geese, Amelia and Abigail Gabble, who accompany the cats to Paris. Edgar returns to the country to retrieve his possessions from Napoleon and Lafayette, as the only evidence that could incriminate him.
Travelling across the rooftops of the city, the cats meet O'Malley's friend Scat Cat and his musicians, who perform the scat song Ev'rybody Wants to Be a Cat. After the band has departed, O'Malley and Duchess converse on a nearby rooftop while the kittens listen at a windowsill. Here, Duchess' loyalty to Madame prompts her to decline O'Malley's proposal of marriage. Duchess and the kittens return to Madame's mansion, but Edgar places them in a sack and prepares to ship them to Timbuktu; whereupon they direct Roquefort to retrieve O'Malley. He does so, and O'Malley returns to the mansion, ordering Roquefort to find Scat Cat and his gang. This done, the alley cats and Frou-Frou fight Edgar, while Roquefort frees Duchess and the kittens. In the end of the fight, Edgar is locked in his own packing-case and sent to Timbuktu himself. Madame Adelaide's will is rewritten to exclude Edgar, with Madame expressing surprise at Edgar’s departure. After adopting O’Malley into the family, Madame establishes a charity foundation housing Paris' stray cats (represented by Scat Cat and his band, who reprise their song).
- Eva Gabor as Duchess - Madame Adelaide's cat and mother of three kittens; but forced to choose between loyalty to Madame and her own attachment to Thomas O'Malley, until the end of the film. Robie Lester provided the singing voice for Duchess.
- Phil Harris as Thomas O'Malley (full name: Abraham de Lacy Giuseppe Casey Thomas O'Malley) – A feral cat who befriends Duchess and her kittens, becoming a father figure to the kittens and falling in love with Duchess.
- Gary Dubin as Toulouse - the oldest kitten, who idolizes all alley-cats and especially Thomas. He is also a talented painter.
- Liz English as Marie - Second-eldest kitten; often imperious or snobbish to her brothers, but her mother's especial companion. Something of a singer.
- Dean Clark as Berlioz - the youngest kitten. He is somewhat timid and shy, but a talented pianist.
- Roddy Maude-Roxby as Edgar Balthazar - Madame Adelaide's butler who tries to get rid of the cats in order to inherit her fortune.
- Scatman Crothers as Scat Cat - Thomas's best friend and leader of a gang of jazz-playing alley cats. Scat Cat plays the trumpet.
- Sterling Holloway as Roquefort - A house mouse and also a friend of the cats, who assists in the expulsion of Edgar.
- Paul Winchell as Shun Gon - a Chinese cat in Scat Cat's gang. Plays the piano and drums made out of pots.
- Lord Tim Hudson as Hit Cat - an English cat in Scat Cat's gang. Plays acoustic guitar.
- Vito Scotti as Peppo - an Italian cat in Scat Cat's gang. Plays the accordion.
- Thurl Ravenscroft as Billy Boss - a Russian cat in Scat Cat's gang. Plays the double bass.
- Pat Buttram as Napoleon - a Bloodhound who attacks Edgar when he intrudes in the farm where Napoleon lives. Napoleon insists, whenever cohort Lafayette makes a suggestion, that he is in command, then adopts Lafayette's suggestion as his own.
- George Lindsey as Lafayette - a Basset Hound and Napoleon's companion. He sometimes proves smarter than Napoleon, but is also more timid.
- Hermione Baddeley as Madame Adelaide Bonfamille - a former opera singer and owner of Duchess and her kittens.
- Charles Lane as Georges Hautecourt - Madame Bonfamille's lawyer: an eccentric, lively old man who provides comic relief by attempting stairs too steep for himself.
- Nancy Kulp as Frou-Frou - Roquefort's horse companion, who subdues Edgar. Ruth Buzzi provided her singing voice.
- Monica Evans as Abigail Gabble - a goose who befriends the cats.
- Carole Shelley as Amelia Gabble - Abigail's twin sister.
- Bill Thompson as Uncle Waldo - the drunken gander uncle of Abigail and Amelia.
- Peter Renaday - French Milkman/Le Petit Cafe Cook/Truck Movers (uncredited)
- Mel Blanc - Frog (uncredited)