This paper focus on the organization building and activities of Korea Army Counter Intelligence Corps(CIC). Republic of Korea Army CIC inherited experience of the U. S. Army CIC. On 9 September 1945, the first agents of the 224th CIC detachment arrived in Korea. The 224th CIC detachment was changed by the 971st CIC detachment. During the American military occupation period, U. S. Army CIC`s major task is investigating activities of left-wing organization. U. S. Army CIC helped set-up of Korean Army CIC. In July 1948, Syngman Rhee and U. S. Army G-2 officers decided that a South Korean organization modeled after CIC should be established. Syngman Rhee has ambitions to establish civil intelligence agency as a official government organization. But this project whicj is called Korean Research Bureau was failed by National Assembly rejection. On May, 1948, the organization which was later to became the Republic of Korea Army unit most closely corresponding to the U. S. Army CIC was founded. The original mission of this unit was to conduct background investigations of government personnel, to maintain surveillance of communist activity in South Korea. This unit which is named Special Investigation Section redesigned Special Investigation Service in November 1948. Most important task of Special Investigation Service is purge of pro-communist elements among the military unit. Special Investigation Service changed its name to CIC. During The Korean War, ROKA CIC engaged many kinds of civilian massacre cases like prisoner massacre. On October 1950, ROKA CIC changed its name Special Operation Unit(Teuk Mu Tae).