Internal audit has an important role in helping a firm to achieve its objective when it isrnimplemented, operated, and managed effectively. Organizations which effectively implemented,rnoperated and managed internal auditing were better able to identify their business risks andrnsystem inefficiencies for the sake of taking corrective actions and improvement in the process.rnThe overall objective of the study is to identify the factors determining the effectiveness ofrninternal audit in Ethiopian commercial banks. The study used purposive sampling method andrncovered the head office internal auditors of Ethiopian Commercial Banks. The study adoptedrnmixed research method by employing quantitative and qualitative research methods. Thernquantitative research method used through 147 usable self administered questionnaires. Thesernquestionnaires were constructed in 5-point likert scale, distributed to internal auditors ofrnEthiopian Commercial Banks, and analyzed using SPSS statistical software. The qualitativernresearch method used through personal interview with internal audit dir ectors of Ethiopianrncommercial banks and selected documents review. According to the results of the study;rnindependence of internal audit, competence of internal audit team, and management supportsrnwere strong and statistically significant effect on the effectiveness of internal audit regarding onrnvalue adding role, enhance department performance, and enha nce organizational performance. Inrnthis regard, independence of internal audit, competence of internal audit teams and managementrnsupports were the factors determining effectiveness of internal audit in Ethiopian commercialrnbanks. The researcher mainly recommended; give attention on the development of certifiedrnpersonnel, top management and IA team work collaboratively in changing audit culture, and tornwork in using IA softwares.rnKey words: Internal Audit, Ethiopian Commercial Banks, and Effectiveness of Internal Audit