The article deals with the activities of Soviet security agencies against former representatives of Siberian Cossack Army on the territory of the Omsk region. This article shows Omsk as the center of the Soviet state repressive politics concerning Siberian Cossack Army. The main activities included shadowing of its representatives, reporting to the party bodies about the situation in the Cossack community and repressive politics against Cossacks representatives aimed at eliminating the Cossacks as social category. We mention factors that caused repressions against Siberian Cossack Army. The repressions were caused by international and domestic political situation, by professional mentality of Soviet security service officers that regarded Cossacks as opposition and by the history of Siberian Cossack Army that became an active force of anti-Bolshevists movement in Eastern Russia during the Civil war. In regard to Siberian Cossack Army the state security bodies pursued repressive policy in accordance with the Soviet State security interests.