Recently, Six Sigma to increase market share , decrease costs, and grow profit margin has been adopted by some leading companies in the world. Six Sigma is expected as the optimal movement to raise the quality level remarkably and to make enterprise culture and organization based on customer and market orientation. In this paper, we study on the idea of Six Sigma, the Internal and external success case, the reliability tools using in the Six Sigma, and the difference between the existing quality movement and Six Sigma. Also, we discuss the role of reliability In Six Sigma..