This study examined the responses of Korean manufacturing firms to the legal mandate for appointing outside directors. Following the 1997 foreign exchange crisis, the Korean government legislated the appointment of outside directors as part of corporate governance reform. During the legislative deliberation process, various employer associations, including the Federation of Korean Industries, strongly opposed the legal mandate for outside director appointments. However, after the legislation was enacted, some listed companies appointed more outside directors than legally required. This study sought to explain the over-appointment of outside directors by these firms from an institutional theory perspective. Hypotheses were proposed that the greater the degree of damage to a firm's social legitimacy, the greater its proximity to the world society, and the greater its visibility, the higher the likelihood of over-appointing outside directors. Analysis of data from 1998 to 2000 tested these hypotheses, and based on the results, the study discussed the theoretical implications for institutional theory, the limitations of the research, and directions for future research.