study for my major part 1. The effect of ownership structure on business performance has been discussed on many previous studies. In this study I focused on the relationship between ownership structure and business performance of Korean Construction companies, and the difference of business performance between owner manager construction companies and employed expert manager construction companies using by analysis of actual proof, since financial crisis in 2008. 33 listed companies for 6 years between 2009 and 2014 are used for this study. To evaluate the effect of ownership structure on business performance, Regression analysis is performed by using Market to Book Financial Ratio(MTB) and Return on Assets(ROA) as measuring variables for business performance. Equity ratio of major shareholders, equity ratio of foreigners and equity ratio of institutional investors(including shareholders who own 5% and above of shares.) were used as measuring variables for ownership structure. And debt ratio, liquidity ratio(cash holding ratio), firm size were used as control variables. With regard to the additional selection, conglomerate status were not used as dummy variables due to all the sample companies are affiliated to their own group. In addition to the effect of ownership structure on business performance, T-test were implemented to find out the difference of business performance between construction companies managed by owners and employed expert managers.