SUMMARY
The aim of this paper is to analyze the effects of internal control system on Tax revenue internal audit performance in Ministry of Revenue Hawassa and Jimma town districts. The study used explanatory research design and analyzed the primary data using a multiple regression analysis on SATA 14 software package. The regression analysis results exhibited control activities, control environment and information and communication components were significantly affecting tax revenue audit performances of Southern and south western regions of ministry of revenue main offices in Ethiopia. Based on the findings of this study, the researchers recommended that it is better if Ethiopian ministry of revenue strengthen its control activities in strategic manner because good control activities easily responds to the dynamic situation with the full potential and prevent frauds & misappropriations of public assets. Moreover, to foster a tax revenue internal audit performance, since tax auditors need relevant, timely and persuasive evidences that really reflects the fairness of the organizations’ position and promotes reporting reliable financial reporting, organizational structures need to be integrated and coordinated by establishing effective information and communication dissemination systems.