A common HIS (Hospital Information System) database schema which follows international medical EDI standard can reduce data conversion between heterogeneous medical databases when they exchange medical information. This method can also make it more convenient to keep data integrity and accuracy after data are transferred. Based on this idea, a common metadata schema and data schema for HIS databases are proposed. In order to develop schema according to Health Level Seven (HL7) that is expected to be an international standard, entities and attributes are extracted directly from HL7's data fields. Furthermore this thesis develops a metadata schema that covers four areas - data management, application management, activity management and infrastructure management - and data schema that covers seven areas -steps, patient, insurance, order, schedule and case-.