With the increasing importance of EC (Electronic Commerce) across the Internet, the need for agents ro support both customers and suppliers is growing rapidly. But the lack of standard on product ontology, message and negotiation protocol between agents and brokering makes full automation of EC infeasible. In this paper, we describe an open infrastructure for agent-based EC and design a virtual market server. As an open infrastructure, we propose a complete architecture and message protocol for inter-agent negotiation. We designed and partially implemented a virtual marker server, named ICOMA (Intelligent electronic COmmerce system based on Multi-Agent) based on the advanced agent technologies. The goal of ICOMA, is to construct the decentralized dynamic, and diverse EC environment.