The purpose of this study is to examine the factors determining the performance of the internal audit (IA) in the context of internal auditors' work environments. This includes Enterprise Risk Management (ERM) implementation, the Enterprise Resource Planning (ERP) system, the use of auditing software and the internal auditors' IT (information technology) competence. Although a number of recent studies have reported tremendous changes in the roles of the IA, there is still little research on the influential factors of IA implementation and its effectiveness from a contextual perspective. This paper develops and tests a theoretical framework with samples from Taiwan. Data were analyzed using the structural equation model (SEM). This research confirms that the complete ERM implementation and effectiveness of ERP implementation have significant impacts on the performance of IA. It also highlights the importance of internal auditors' IT competence in improving the performance of IA.