Health Level Seven(HL7) is a standard protocol for electronic data exchange in healthcare environments. We implemented HL7 interface engine, for unifying medical records between heterogeneous hospital databases. As a HL7 message toolkit, we modified ProtoGen/HL7 C++ class library from World Wide Web. The whole system is composed of two modules, the client module and the server module. The client module accepts user's requests, and builds them into HL7 message stream. The server module parses this data stream, searches the requested data and then sends them to the client module for displaying. Healthcare professionals can find the patient's medical data from two hospital databases by typing patient's name and patient ID. This test confirms that HL7 interface engine can be used meaningfully in our clinical system.