Jab Pyaar Kisise Hota Hai is about one Sooraj Dhanrajgir (Salman Khan), a rich playboy lightening the financial burden of his industrialist grandfather (Anupam Kher) by spending his riches on alcohol and women. His grandfather calls him back for some official work back home, beginning with a hotel project in Ooty. There his true character emerges as he starts running after pretty girls. The first girl he lays his eyes on happens to be Komal (Twinkle Khanna). He convinces her that she is his childhood friend and sweet talks her into falling for him. But soon she sees him for the player he is and walks out on him.
However, for once Sooraj is smitten beyond infatuation and knowing she runs a boutique in a hotel somewhere in Bombay, he goes through the hotels of the city until he locates her. He tries his best to win her back but he fails. Sooraj's grandfather steps in to ease the situation and asks her to marry him. Komal agrees, on one condition that he would have to give up his playboy status and become straight which meant he would have to quit smoking, drinking and women for her to marry him. Sooraj, not quite the man he was, gives up every bad habit he has. Finally Sooraj returns home one day and he find a boy, Kabir (Aditya Narayan), claiming to be his son.
Tests prove that Kabir is indeed his son, but Sooraj doesn't even remember the mother. Kabir shows him a photograph which Sooraj helps identify the women he had a fling lasting a few months. He brings the boy back, identifying him as his friend's child. Sooraj learns to like him, and gradually, understanding his mistake, he recognizes him as his son. But Kabir never really liked Komal. Kabir is also unhappy to learn that Sooraj never really loved his mom.
Later Sooraj has to choose either Komal or Kabir. Sooraj is about to get married to Komal however knows that he cannot hide the fact that Kabir is his son from Komal for longer time he falls into a dilemma. His friend Mahesh suggests him to tell all the truth to Komal about Kabir before marriage if he really loves her. He try several times to speak to Komal over phone to inform that Kabir is his son but circumstances does not allow him to speak and convey the message over phone.
The day on which Sooraj and Komal about get married, He lands at her house before mahurat with his grandfather, friend and son Kabir. He honestly accepts all his mistakes he made in life and tells Komal and her family that Kabir is his own son. On hearing this Komal family gets angry and demands Sooraj to disown Kabir if he wants to marry Komal. Sooraj refuses to do that and prefer to choose son over his love but Komal decides to marry Sooraj despite knowing that he has a son. She hails Sooraj's honesty and agrees to accept Kabir as her son.