According to prior literatures, insiders manage earnings downward before they buy shares of their firm and they manage earnings upward before they intend to sell their owns because of benefit from increasing or delaying stock prices(Kim et al. 2010). Corporate governance characteristics, such as foreign investors’ ownership, institutional investors, and established audit committees, effectively mitigate manager’s opportunist earnings management before insider trading(Lee and Hwang 2013). Many prior research states that independent board can effectively monitor and control manager’s earnings management or insider trading. However, there is some doubt about independence of board because blood relation, regionalism and school relation are considered to be very influential in Korea. Therefore, this study examines whether real independence of board mitigates insiders’ opportunist earnings management before engaging in insider trading. Our sample consists of 2,150 firm-years over the 2009-2012 period. The findings of the study are as follows: First, there is a positive association between social tie within board member and insider trading. Similarly, real independent outside directors who have no tie such as regionalism, high school, university effectively control and monitor insider trading. Also, there is a positive association between social tie and manager’s earnings management before engaging in insider trading, especially high school tie and outside directors with no tie mitigate manager’s opportunistic behavior. These findings suggest that the higher social tie, the stronger bond within board and then these social ties attenuate monitoring of board. When there are high school alumni among directors, boards are more likely to make managers engage in insider trading and opportunist earnings management related insider trading. Given the age range of board members, there is a stronger emotional bond with high school than other ties possibly because they entered high school through competitive entrance examination. The reason why high school tie is the strongest is that high school is relatively small, compared with university and they share the same cultural and generational characteristics of the area where the high school is located in. Most prior studies investigated the relationship between independence of board measured by outside director ratio on the commercial law and manager’s opportunistic behaviors. In comparison, this study collected individual characteristics associated with region and schools and made a score of social tie within board members. We then identified the effect of social tie and real independent outside directors on insider trading and earnings management. Our results provide evidence that many firms appoint outside directors who have tie associated with region, high school, university and graduate school although regulation authorities force independence of board. These dependent boards may connive manager’s opportunistic behavior. This paper shows that real independent outside directors can mitigate insider trading and earnings management before engaging in insider trading. The results of this study suggest that the improvement of board independence is important to ensure the transparency and justice to vitalize capital market.