Real world lives in the ‘Aeon’ of virtual connectivity; social network is a platform where people share emotions, activities, relation etc. Second generation online social networking online comes in existence with service-oriented environment, In which lots of service requester and service provider, connect to each other with many different paths. Among ‘N’ number of path finding a trust path for trustworthy services is major task. In this paper with the help of ant colony optimization (ACO) we are calculating trust path, trust cycle. Hence we are proposing an algorithm (Trust-ACO) to calculate trust in online social network. Trust calculation is based on probabilistic trust rule, social intimacy pheromone.