The story of HUM AAPKE DIL MEIN REHTE HAIN opens with Vijay Chopra (Anij Kapoor) returning from the USA to join his family business. The only son of the widower industrialist, Vinwanath Chopra (Anupam Kher). Vijay carries home with him the attitudes of the Western world, some good like equality of man and woman in a relationship, and some bad, like failure to recognise marriage as an institution.

Vinwanath Chopra hopes to bring some stability into his son's life through marriage and Vijay is all the more reluctant to tie the knot. A compromise is finally struck between the father and the son with Vijay agreeing to marry, with one condition. If he is not compatible with his wife after a year of marriage, he will leave her.

Though disgusted and furious with the condition, Vinwanath Chopra realises that a marriage with a condition is better than no marriage at all. But which girl in her right senses would marry a person who wanted to sign the one year compatibility contract? Vinwanath Chopra feels that there is no one better than Megha (Kajol), his trusted and efficient secretary who is capable of changing his son's heart within a year of the marriage.

Megha (Kajol) is the sole breadwinner of a middle class family. Even though she finds the one year disgusting, the lure of settling her family plays an important role in deciding to marry Vijay. In the one year of marriage, Megha realises that Vijay is not a bad husband at all, he treats her as an equal partner in a marriage and gives her the respect and privacy of an individual. The year just flies by and extremely happy Megha and her father in law Vinwanath Chopra believes that Vijay has finally turned around to believe in the institution of Marriage. Sadly Vijay thinks otherwise and on their first anniversary, he enforces the contract. His explanation is that he and Megha are more friends than husband and wife. Megha leaves his house and goes back to her mother's house. She finds a job in another firm and starts working again. Once the society realises that Megha's marriage was a one year contract, they make fun of her. When Vijay realises what is happening in Megha's life, he wishes to take her back as his wife. However Megha refuses point-blank to move back to a man who does not know the value of marriage.

Vijay tries every trick to woo his lady love. He buys out the company she works for, he organises music shows with her favourite artists, he wears her favourite colours etc. In the midst of all these, Megha realises that she is pregnant with Vijay's child. Vijay is elated and so is his father. But Megha still refuses to go back to Vijay. She is ready to acknowledge Vijay as the father of her child, but not as her husband anymore.

Whether Vijay succeed in winning Megha's heart will be revealed only on the silver screen in HUM AAPKE DIL MEIN REHTE HAIN