The supplier performance has a significant effect on the competitiveness in implementation Just-In-Time and entire supply chain. In this paper, the supplier performance effected in Just-In-Time implementation was described, the supplier must be introduced and developed before being an approved Just-In-Time supplier. Considering, the importance of supplier performance as a part of Just-In-Time implementation, the Just-In-Time will not be successful if no good cooperation from supplier in term of quality and business point of view. This paper proposed the strategies in managing vendor called Vendor Management System (VMS), which shown in the management flow model for development the supplier performance to reach ready state before entering the Just-In-Time. The Vendor Management System (VMS) identifies five phases starting from qualification, measuring, analyzing, implementing and maintaining the supplier performance. The Vendor Management Team (VMT) will implement each VMS phase as proposed steps at a periodic timeframe. The suppliers who reach the ready state level as company goal and expectation will be selected to enter the Just-in-time program. An example of vendor management model in an electronics manufacturer in Thailand showed the effectiveness of the system through the yearly performance and incoming quality lot acceptance rate.