Service Oriented Architecture(SOA) is an enterprise-scale IT architecture for linking software resources available on the network. SOA is believed to become the future enterprise solution that promises the agility and flexibility by integrating business processes through composition of the software services across enterprises. The first step for SOA construction is to identify the services. In this paper, we present a process-based service identification methodology for SOA through a case study of an IT company. Our methodology is composed of three steps: Processes (business & technical processes) analysis and systems analysis, Service candidates selection, and Service evaluation and construction planning. This framework would be practical and could be accepted to other organizations as it has been developed through the real case.