Nowadays many enterprises build e-procurement systems. An e-procurement is a Web-based procurement process and its functionalities are considered important in the B2B e-commerce. Buyers should select competent suppliers for a successful e-procurement. Therefore, this study proposes a method using the analytic hierarchy process(AHP) for building a Web-based supplier selection system. In detail, the purpose of this study is (1) to review methods previously used when buyers selecting suppliers and to extract important selection criteria： (2) to explain extended AHP method adopted by this study among supplier selection methods： (3) to describe the supplier selection steps using extended AHP ： and (4) to propose a decision support system embedding the methodology described above. The proposed system comprises of three phase： first phase is to evaluate suppliers on enterprise level： second phase to evaluate them on each transaction level： third phase to post-evaluate them.