As the semantic web application grows, the amount of semantic data with the RDF(Resource Description Framework) format is rapidly increasing worldwide. A scalable and robust access mechanism for distributed RDF data is necessary. To solve the problem, we developed a middleware called OGSA-DAI-RDF, which is based on the grid standard architecture OGSA(Open Grid Services Architecture). By using OGSA-DAI-RDF, users can easily federate distributed RDF databases using the SPARQL standard language. This R&D activity is tightly linked with the OGF(Open Grid Forum) working group activity to set the access specification of RDF databases.