In todays, world key management for secured cloud is very essential. Dealing huge data on computing is one of the major requirements of the modern computing. This paper proposes ant colony based authentication mechanism for cloud system. Ant Colony Optimization (ACO) is a swarm intelligence technique. ACO provides optimality in many discrete mathematical problems in almost all engineering problem domains. ACO follows the imitation of behavioral aspects of ant. Recent researchers highly following swarm intelligence algorithms for critical and real time problems. Secured cloud is an important research issue due to its variety of customers, devices used for access, variant parameters and metrics involved.