Rajadurgada Rahasya ( ) is a 1967 Indian Kannada-language film, co-directed by A. C. Narasimha Murthy and S.K.Bhagwan, and produced by A. Vasudeva Rao and T. Dwarakanath. The film stars Rajkumar, Bharathi, Udaykumar, Narasimharaju and Dinesh, with a musical score composed by G. K. Venkatesh. Rajkumar plays dual roles in this film. Although S.K.Bhagwan was the primary director, he revealed that the directorial credit was shared with Narasimha Murthy, who was the chief financier of the film. The film was later dubbed in Tamil as Malaikotai Marmam. This was also the final film in which Bhagwan directed actress Bharathi Vishnuvardhan.
The music was composed by G. K. Venkatesh.