This paper examines the relationship between corporate ownership structure in Korea and the informativeness of earnings. Korean ownership structure is characterized by the dominance of one primary owner who also participates in firm management. Existing literature offers two alternative perspectives on the behavior of such owner-manager, convergence of interests and management entrenchment hypotheses. We tested how the alternative views are reflected in earnings informativeness. The results show that earnings are more informative as holdings of the owner increase, supporting the convergence of interest explanation for the owner-manager. Second, we examine the role of institutional investors and blockholders. On the one hand, institutions/blockholders have incentives to actively monitor management. However, on the other hand, institutions/blockholders may not render effective monitoring because they lack expertise, suffer from free-rider problems, or strategically ally with the management. These opposing views predict conflicting signs on the relation between the earnings informativeness and holdings of institutions/blockholders. We find that earnings informativeness increases with the holdings of institutions and blockholders. This supports the active monitoring role of institutions/blockholders. Finally, we test the relationship between earnings informativeness for chaebol (Korean business group) affiliated companies versus that for non-chaebol affiliated companies, and