Multinational corporations (MNCs), which have grown rapidly since the Second World War, play a critically important role in the world economy, and their significance will continue to increase as global integration accelerates. Due to their structural characteristic of maintaining subsidiaries abroad, MNCs inherently face considerable uncertainty. Accordingly, extensive research has been conducted on MNC control, yet most studies have focused on phenomenological analysis without a solid theoretical foundation for control. This study attempts an in-depth analysis of MNC control grounded in agency theory. The research examines multinational corporations from the United States and Japan—Korea's major investment partner countries—and yields the following findings. First, the degree of parent company ownership has a positive effect on the level of agency control (output control and cultural control). Additionally, the effect of ownership structure on output control is mediated by the subsidiary's relative size (in terms of capital and number of employees) among various subsidiary characteristics. The nationality of the parent company also influences control types, with Japanese firms exhibiting higher levels of cultural control, and these control types maintain mutually independent relationships. Overall, this paper demonstrates that agency theory, when integrated with existing cultural and strategic studies, provides a highly useful explanation of MNC control.