This paper examines the relationship between the degree of busyness of independent director and the variability of firm performance. The relationship between the number of directorships per independent director and the variability of firm performance is unclear before considering firm characteristics. However, after taking the characteristics into account, we find that independent directors on boards with higher level of independence have better reputation and provide better monitoring function. They make moderate decisions to reduce the performance variability; remove CEOs owing to their poor performance. Professional expertise of independent directors does not reduce variability of firm performance; however, busy independent directors with law, business, politics or industry-related experience backgrounds can effectively monitor the firms.