Service-Oriented Architecture (SOA) is emerging as a promising technology for changing the way to build internal systems and to interact with inter-organizational systems. When SOA technology is applied, however, it's difficult to adopt directly existing software system development methodologies, because of the primary elements such as services and flows. A critical step in the process of developing applications based on the SOA is the service modeling. This paper shows how services can be identified from the business Usecase model. This paper introduces processes and guidelines to support the service modeling. The benefit of the proposed identificaiton method is that the service has reflected the business of the domain well and is in its proper granularity. The assessment guidline can help the settlement of a problem that is to determine the implementation strategy.