This study follows the definition of Taiwan Stock Exchange Corporation to select the director and supervisor's self-interest companies and investigate the relationship between the self-interest behavior of directors and supervisors and the core agency problem. The results show that companies with higher degree and probability of self-interest behavior of directors and supervisors are usually characterized by the lower ownership of directors and supervisors, worse TCRI rankings, lower cash flow rights or greater separation between the control rights and cash flow rights of the controlling shareholders. In addition, the companies fully controlled by the controlling shareholders also have a higher degree of self-interest behavior of directors and supervisors. The companies with low outside directors and supervisors, due to core agency problem and weak corporate governance mechanism, are more likely to have self-interest behavior of directors and supervisors. On account of the unique ownership structure of Taiwanese companies, it's not hard to observe the self-interest behavior of directors and supervisors. The findings of this study may help us better understand the relationship between the self-interest behavior of directors and supervisors and core agency problem.