Kiki is a 13-year-old witch-in-training, living in a village where her mother is the resident herbalist. It's traditional for witches to live for a year alone when they reach 13. In the opening of the story, Kiki takes off for the big city with her best friend, Jiji, a loquacious black cat.
Kiki settles in Koriko, a beautiful city by the sea. After a hard start, mostly because of her own insecurity, Kiki finds friends and a place to stay. But she has only one witch's skill: her magnificently natural ability to fly; so in order to support herself, she begins a delivery service.
Kiki experiences setbacks, and she must contend with adolescent worries. She is pursued by Tombo, a local boy who's crazy about aviation and has developed a genuine respect for her flying power and a strong liking for Kiki as a girl in general. Kiki eventually warms up to him, but after an unpleasant encounter with Tombo's friends, some of whom she had met earlier under unfavorable circumstances, Kiki's powers to fly and speak with Jiji suddenly diminish and ultimately disappear, leaving Kiki devastated. However, one of her friends, a young painter named Ursula, invites her to stay in her forest cottage, where she analyzes Kiki's current crisis as some form of "artist's block." Since many things had not gone as hoped for, Kiki is experiencing a period of insecurity and loneliness, which resulted in the loss of her powers; but if she finds a new purpose, she will be able to reclaim what she has lost.
Heartened, Kiki returns to the city. While visiting one of her customers, she witnesses an accident in which Tombo is lifted into the air and blown away hanging from a dirigible. In her desperation to save him, Kiki pushes herself to regain her flying ability. Improvising with a street-sweeper's push broom, Kiki manages to reactivate her power and rescue Tombo.
The story continues through the end titles where we see that Kiki is now comfortably part of the life in Koriko as its own local celebrity. She flies in formation with Tombo on his human-powered aircraft. The film closes with Kiki sending a letter to her parents about gaining confidence through difficulties and that she has decided to make this city her new home.