The case was filed by Shefali Sarkar, widow of former Barabani MLA Dilip Sarkar, in the court of additional chief judicial magistrate, Asansol.
Dilip (65), was shot dead by four motor cycle borne assailants near Asansol on June 9 during morning walk.
The CPI(M) blamed the Trinamool Congress for the murder, and Roy, while denying the accusation at a press conference in Kolkata on the same day, allegedly made some defamatory statements.
As no reply came from Roy, the defamation case was filed which was admitted by the ACJM, the lawyer said.