- Salman Khan: Anand
- Kareena Kapoor: Dr. Tanvi Khurana
- Rimi Sen: Maya
- Jackie Shroff: Dr. Sunil
- Om Puri: Dr.Khurana
- Sunil Shetty: Karan ( guest role )
The widowed Colonel Khurana runs his private psychiatric hospital where his daughter Tanvi is working as a doctor. The inhumane treatment of the mentally ill, who practiced Khurana, not just serving their recovery. Tanvi is more humane than her father and takes special care to the patient # 36, as if she were their own mother she never had. The patient also viewed almost as a daughter, as long as it relies on Tanvis help. But when she is finally healthy, she shows herself very ungrateful and leaves the clinic to say a kind word without Tanvi. Tanvi is therefore very offended and decides never to close their patients to the heart. From now on, they treated the sick not much better than her father. Particularly hated by her is the new patient # 36 - Anand Sharma, who is accused of the murder of his wife, but was told by the court for debt unfit because he is supposed to be mentally disturbed after the fact. Dr. Sunil, who also works at the clinic, is the son of a domestic worker of the Sharma family, who got financial support from Anand's father during medical studies. Anand, with whom he grew up, was always like a brother to him. That's why he is trying to protect Anand from the cruel treatment. He also draws Tanvi to his side, by revealing her Anand's love story:
Some time ago, Anand has fallen in love with Europe in a convent girl named Maya, who sang in the church choir and was about to become a nun. Anand has tried everything to win her affection. Ultimately, he was successful, and Maya was to his wife. He brought them to India to introduce her to his relatives and friends, but during the party is a disaster happens. Anand Maya threw into the pool without knowing that they can not swim. When he realized that it was too late - Maya was drowned. This Anand suffered a mental disorder.
When Tanvi learns the story, she feels attracted by Anand and slowly falls in love with him. Thanks Tanvis and Sunil's efforts Anand comes to its own and must be discharged from the hospital soon. He is also in love and wants to marry Tanvi. But her father has already promised the Karan who is currently with them for a visit. The Colonel is willing to do anything to prevent his daughter from marrying Anand.
Kyon Ki is Priyadarshans remake of his Malayalam film Thalavattam (1986 ) with Mohanlal in the lead role.