The article examines how ownership structure affects financial performance in South Korean companies. It looks at two main aspects of ownership: how many shares majority owners have and who the owners are. The study found that as ownership concentration increases, firm performance generally gets better. However, having too much ownership concentration can lead to negative effects like mistreating minority shareholders. Foreign and institutional ownership didn't show significant effects on performance. The research suggests that there is an optimal level of ownership concentration for best performance in companies. This information can help policymakers improve corporate governance in South Korea.