Abstract: Free space optical communication provides a very important method for the satellites orbiting around the earth to communicate with each other. Inter-satellite optical wireless communication systems (IsOWC) are one of the important applications of FSO/WSO technology that will be expand in space in the near future. These systems provide a high bandwidth, small size, light weight, low power and low cost to present microwave satellite systems. In this paper, optical inter-satellite link (ISL) is modeled using optisystem software between two satellites separated by a distance of 1700 km at data rate 3 Gbps at varying modulation formats.