Ten-year old Chihiro and her parents are moving when her father takes a wrong turn. Her father thinks they've found an abandoned amusement park and insists on exploring. Chihiro, scared to be alone, accompanies her parents.
They cross a dry riverbed. Chihiro's parents gorge themselves at an unattended restaurant stall while Chihiro wanders off. She finds an exquisite bathhouse. Suddenly a boy orders her to cross the river before dark. Spirits begin haunting the park, and when Chihiro returns to her parents, they have become pigs.
Chihiro runs to the river, but it has flooded and is impossible to cross. The boy, whose name is Haku, finds her and says he has known her since she was little. He tells her to ask for a job from the bathhouse's boiler-man, Kamaji. Kamaji and the worker Lin send Chihiro to the witch Yubaba, who runs the bathhouse. Yubaba gives Chihiro a job but steals her name. She is renamed Sen
(千?), the first character of her name.
Haku shows Sen her parents' pigpen. Among her belongings, she finds a goodbye card addressed to Chihiro. Sen realizes that she has already forgotten her name. Haku warns her that Yubaba controls people by taking their names. If she forgets hers like he has forgotten his, then she cannot leave the spirit world.
At work, Sen invites a silent masked creature inside. A stink spirit arrives and is Sen's first customer. She discovers he is the spirit of a polluted river. In gratitude for cleaning him, he gifts Sen with a magic emetic dumpling. Secretly, the masked creature tempts a worker with gold, then swallows him. Publically, the creature demands food and begins tipping extravagantly.
The next morning, Sen sees paper shikigami attacking a dragon. She recognizes the dragon as Haku transformed. When Haku crashes into Yubaba's penthouse, she runs upstairs. As she passes the masked creature, he offers her a heap of gold, but she refuses it.
When Sen reaches Haku, a shikigami that stowed away on her back transforms into Zeniba, Yubaba's identical twin sister. Zeniba turns Yubaba's baby son Boh into a mouse and creates a decoy baby. Haku has stolen a magic gold seal from her, and she warns that it carries a deadly curse. Haku dives to the boiler room with Sen and Boh on his back. As they fall, Sen has a memory of being underwater. She feeds Haku part of the dumpling, and he vomits up the seal and a black slug that Sen crushes. She resolves to return the seal and apologize for Haku.
Before she leaves, she confronts the masked creature, who is a monster named No-Face. No-Face has become disgustingly obese, so Sen feeds him the rest of the dumpling. He begins vomiting and angrily chases Sen out of the bathhouse. As he vomits, he returns to a normal size and a gentle demeanor.
While Sen, No-Face, and Boh travel to Zeniba, Yubaba is furious at the damage caused by No-Face. She blames Sen for inviting him in and orders that her parents be slaughtered. Haku prods her into realizing that her baby is missing. He proposes to return Boh in exchange for Yubaba freeing Sen and her parents.
Sen, No-Face, and Boh arrive at Zeniba's house. Zeniba reveals that Sen's love for Haku broke her curse. The black slug was how Yubaba controlled him. Haku arrives. As he flies her and Boh back to the bathhouse, Sen has another memory of being underwater: When she was little, she fell in the Kohaku River but was washed safely ashore. She realizes that Haku is the spirit of the Kohaku River and tells him his name.
To break the curse on her parents, Sen must recognize them from among a group of pigs. She correctly discerns that her parents are not there. Haku takes her to the riverbed, which is dry once more. He says that he can't come with her, and she must not look back, but they will surely meet again.
Chihiro's parents are waiting for her on the other side. They do not remember anything and scold her for wandering off. They walk back to their car, which is filled with dust.
