A lieutenant commander assigned to the Defence Security Command faces charges that he handed over classified information to a suspected Chinese agent while he was studying in China from 2009 to 2012.
He allegedly passed military materials to a university student in return for money.
South Korean authorities suspect the Chinese student was a spy.
Last month, two officials of the Defence Security Command were sentenced to six years and four years in prison respectively for passing classified information to arms dealers.
The incidents have dealt a blow to the Defence Security Command, whose tasks include the prevention of espionage and the establishment of discipline within the military.