As is traditional for trainee witches, thirteen-year-old Kiki leaves home with her black cat named Jiji, whom she can understand. She flies on her broomstick to the port city of Koriko. While searching for somewhere to live, Kiki is pursued by Tombo, a geeky boy obsessed with aviation who admires her flying ability.
In exchange for accommodation, Kiki helps Osono, the kindly and heavily pregnant owner of a bakery. She opens a “Witch Delivery Business”, delivering goods by broomstick. Her first delivery goes badly; she is caught in a gust and loses the black cat toy she is supposed to deliver. Jiji pretends to be the toy until Kiki can retrieve the real item. She finds it in the home of a young painter, Ursula, who repairs and returns it to Kiki so she can complete the delivery and rescue Jiji.
Kiki accepts a party invitation from Tombo, but is delayed by her work and, exhausted, falls ill. When she recovers, Osono clandestinely arranges for Kiki to see Tombo again by assigning her a delivery addressed to him. After Kiki apologizes for missing the party, Tombo takes her for a test ride on the flying machine he is working on fashioned from a bicycle. Kiki warms to Tombo but is intimidated by his friends, and walks home.
Kiki becomes depressed and discovers she can no longer understand Jiji, who has befriended a pretty white cat. She has also lost her flying ability and is forced to suspend her delivery business. Kiki has a surprise visit from Ursula, who determines that Kiki’s crisis is a form of artist’s block. Ursula suggests that if Kiki can find a new purpose, she will regain her powers.
While Kiki is visiting a customer, she witnesses an airship accident on television which leaves Tombo hanging from one of the drifting vessel’s mooring lines. Kiki regains her flying power and manages to rescue him. She regains her confidence, resumes her delivery service, and writes a letter home saying that she and Jiji are happy.