This paper empirically examines the effect of corporate governance on operating performance for Korean listed companies over the period 2003-2012. It employs the 2 stage least square procedure to control for potential endogeneity of corporate governance variables. This paper uses as a proxy for corporate governance various evaluation scores which the Korea Corporate Governance Services partly announces recently. Our empirical results show that corporate governance should be positively associated with firm profitability for which return on assets is used as a proxy variable. The corporate governance scores are found to be endogenous and thus simple OLS estimation of the model by ignoring the endogeneity of the variable can produce biased results.