Santosh is a family drama. A rich and cold-hearted woman named Kamla (Nirupa Roy) falls in love with a poor man and marries him, the couple has a son named Santosh (Manoj Kumar). However, she is unhappy with her poor lifestyle, thus she abandons her husband and son to marry a rich man. Later, she has a son named Kundan (Prem Chopra) from her second husband. Santosh starts to work in the mill run by Kamla, while she is unaware that he is her son. Santosh sides with the mill workers, who are wronged by Kamla, while she turns her goons and Kundan against Santosh. Thus, the half-brothers become the rivals. Will the situation become any better when the brothers learn the truth?