Saranya, a school teacher, was attacked by 28-year old Shiva, son of her father's younger brother, with a knife in the neck and stomach in the presence of her mother and sister at her house in Kondanayakanpatti near Andipatti.
She was rushed to a hospital but died without responding to treatment.
Shiva, who fled the scene, was later arrested, police said.
She had explained to him that since he was her brother, by relation, it was not possible to marry him, but he entered into arguement with her and then suddenly stabbed her, police said.