The purpose of this study is to explore the influences of internal and external environmental pressures on corporate performance. In addition, this study would like to discuss the mediation role of green core competence between internal environmental pressure and the corporate performance. The aim is to find the correct evaluation and position for internal and external environmental pressures. Another key issue of this research is to verify whether green core competence plays a mediation role between external (or internal) environmental pressure and the corporate performance. The research findings show that both of external and internal environmental pressures positively impact green core competence. Moreover, this paper indicates that green core competence positively affects corporate performance. However, we find out that both of external and internal environmental pressures are not significantly related to corporate performance. Hence, this study verifies that green core competence plays a full mediation role between external (or internal) environmental pressure and the corporate performance. It shows that both of external and internal environmental pressures can indirectly affect corporate performance through green core competence, which means that a proper degree of pressure that comes from the environmental protection is of great help to the firms. Internal environmental pressure is different from external one. The former can be controlled by a firm itself. The implication for Taiwanese manufacturing companies is that internal environmental pressure is their first priority to foster and develop.