Following a heated argument with her sister, Kamil killed her last evening, said K P Singh, station house officer (SHO) of the New Mandi Police Station.
He later surrendered before the police and confessed to having stabbed his sister after an argument over her "bad activities" that had tarnished the "family's honour," the SHO said.
The accused was arrested and the body has been sent for a post mortem, police said.