We examines the correlation between firm ownership structure and firm performance of a sample of 5206 pannel data listed on Korea Stock Exchange during 2000-2011. This paper analyzes the correlation of perfomance and ownership concentration with fix effect estimation, Fama-MacBeth, Newey and West and Cluster-in. Following the agency theory, the results suggest the there is a significant relation between firm ownership structure and performance when measured by the Tobin's Q and TFP Considering that the actual degree of control is the result of the shares owned as well as the rest of the shares owned by other types of shareholders, the study also finds significant correlation between degree of control and ROA, Tobin's Q and TFP. The level of correlation varies with the type of the ownership and the measurement methods. Notably, shares owned by blockholder have not a significant impact on ROA but degree of control of blockholder generate a positive impact on ROA The results of this study show that the major variables which are not significantly related to the performance in analysis of ownership structure can have explanatory power in the analysis of degree of control. In addition, they indirectly prove that the voting rights of shareholders and substantial managerial control in corporations can be different.