Even though several methodologies for SOA(Service Oriented Architecture) have been proposed, in practical aspects most of them have some problems since they fail to propose specific policies in definition and identification of a service. This paper proposes a service modeling methodology. SOMO(Service Oriented Modeling using Ontology), which draws proper services in the process of defining and identifying services. SOMO defines a service ontology based on service definition and characteristics in SOA. The service drawing process consists of 3 steps : requirement analysis, service identification, and service definition. SOMO is expected to increase the degree of reuse and facilitates the definition and search of services by using service ontology. In addition, it clearly allows the definition and identification of services, satisfying the user requirements.