In this paper, we propose a WebSIS which provides various semantic information services based on web service and ontology for Grid computing environment. The prototype of WebSIS provides resource information service for resource discovery, resource matching and resource monitoring, in order to allocate appropriate resource for user task. Since WebSIS creates a Virtual Organization by defining a resource pool which consists of ontology instance data, it can build a extensible and scalable resource pool dynamically by creating and deleting ontology instance data for each resource. Moreover, the hierarchical structure of ontology and the separate description of schema, instance and rule enables users to build flexible and extensible knowledge base for various domains. We present an extensible and flexible architecture of WebSIS which can efficiently create a new information service and can easily add a new ontology domain. It allows users to build a manifold and reliable information processing service by enabling the incorporation of various semantic ontologies for the inference of semantic information. Moreover, it provides reliability and accurate resource related service by using dynamic resource information obtained through resource agent. We shall show how the semantic information service for resource discovery, resource matching and resource monitoring is carried out in WebSIS.