Today, the company is trying to improve for business performance through the optimization of corporate resources. Most companies set up new strategy for obtaining competitive advantage for survival in rapid changes of the global business environment. IT has an important role to reduce cost and to increases business performance such as increasing sales, improving business skills and corporate image, etc. in the corporate environment. The development and use of IT resource is recognized as essential in connection with the business strategy. Most companies tried to establish the strategic use of information systems to gain competitive advantage. IT resource management is not clear in a tangible result of the business. The purpose of this study is to find out the relationship between IT competency and organizational performance through the mediating effect of strategic use of IS. IT competency consists of IT human resource, IT infrastructure, and IT vendor management. In direct relationship between three IT competence factors and organizational performance, the results of multiple regression analysis showed that IT human resource and IT vendor management are important determinants to influence organizational performance. The additional analysis for mediating effect of strategic use of IS showed that it has mediated the relationship between IT competency factors and organizational performance. This results give us an implication, not only the importance of IT competency development, but also the importance of strategic alignment of strategic use of IS with business strategy.