Many companies are using EDI (Electronic Data Interchange) for the electronic transmission of documents and information to and from other companies. The appearance of Internet can enhance existing EDI systems. Existing EDI systems have several problems such as poor system interoperability and high expense of VAN. This paper prognoses a new EDI system utilizing Internet to provide open communication environment by using XML (extensible Markup language) and this applies it to the EDI service for Hospital Demand. XML is a mark-up language extending HTML which is a standard language for the expression of WWW (World-Wide Web) pages. XML is more structural than HTML, thus it is more suitable for the repetitive tasks of EDI and for the maintenance of databases. XML can transmit EDI documents in the open communication environment of Internet and users can easily access the documents with web browsers. Therefore we can provide EDI services within more open environment and we can build an EDI system with lower expense.