Cloud computing has become a main medium for Software as a Service (SaaS) hosting as it can provide the scalability a SaaS requires. In the composite SaaS placement process， it should consider the factors about the size of the cloud network, SaaS interactions between its components and SaaS interactions with its data components. A previous research has tackled this problem using a genetic algorithm (GA) approach. This paper proposes an ant colony optimization (ACO) approach. The ACO for the SaaS placement problem has been implemented and evaluated.