Support for negotiations is an important issue in today?s collaborative commerce (c-commerce) research. Based on the analysis of state of the art of negotiation support system, and aiming at the environment of c-commerce, we present a web based negotiation support model in this paper. Firstly, we provide a framework for c-commerce. Then, we develope the web based negotiation support model for c-commerce. A protocol for web based negotiation has been provided. The protocol is composed of negotiation entity, commerce rules, and agreement, and is formatted in XML Schema. Based on the negotiation protocol, the negotiation entities can be used to formulate their commerce rules, resulting in an agreement through the automatic matching of their commerce rules.