This paper attempts to identify empirically whether the certification of Quality Management System affects positively to firm performance using the sample sets of 200 SMEs in Korea who have adopted ISO 9000 majoring in the domestic markets as well as the overseas markets. The empirical study has been done on the assumptions and the hypothesis that the certification itself can conceptually and practically be considered an effective tool to improve the level of standardization of quality management system, and it would result in higher productivity and good corporate image by enabling firms to strengthen up their capabilities to achieve competitive advantage. The empirical findings show that the ISO 9000 has positively contributed to not only obtaining competitive advantage but also bringing about a superior firm performance as it would be, making sure that the certification itself would be used as a powerful tool for good management. This study also pinpoints that the success/failure in introducing & adopting the certification depends highly upon the managers' interests and concerns, especially the CEO's.