We investigate the National Property Administration and National Taxation Agency to explore how the execution of the government's internal control system affects governmental effectiveness. In addition we examine the mediating effect of organizational role stress between the internal control system and organizational effectiveness. The questionnaire survey method and linear structural equation model are used to analyze the research samples. The empirical results show that the implementation of an internal control system increases, but role stress decreases organizational effectiveness. However, the implementation of an internal control system can decrease role stress. Results also reveal the partial mediation of role stress, and suggest that the execution of an internal control system can effectively decrease employees' role stress and enhance organizational effectiveness.