It is very important to evaluate the quality of soft wares based on SOA, which develops rapidly. Particularly, one of the most important properties influencing on the quality of system is complexity. Therefore, we propose the metrics for measuring a structural complexity of softwares based on SOA. The proposed metrics is composed of the size of a service, the depth of a service and interdependency from the viewpoint of system structure, and finally we applied the proposed metric to an example.