Abstract: 　　Based on relational exchange theory and transaction cost theory, a conceptual model for the effect of relational mechanism and market contract on knowledge trading among enterprises in supply chain is proposed and empirically tested using the data collected from 256 Chinese manufacturing enterprises in supply chain with the multiple regression models. Relational mechanism is divided into indirect relational mechanism and direct relational mechanism in the paper. Knowledge trading is divided into explicit knowledge trading and tacit knowledge trading. Besides, the indirect relational mechanism is mainly expressed by knowledge broker, while the direct relational mechanism consists of shared goals and trust. The results show that knowledge broker and market contract have significant and positive impact on explicit knowledge trading, but they do not have positive impact significantly on tacit knowledge trading. Shared goals and trust have significant and positive impact not only on explicit knowledge trading but also on tacit knowledge trading, and trust has a stronger positive effect on the tacit knowledge trading than explicit knowledge trading. Finally, it is also proved that market contract has moderating effect on relationships between relational mechanism and knowledge trading.