This study investigated four factors affecting internal audit effectiveness in Vietnam, namely, independence of internal audit, the competence of internal auditors, management support for internal audit, and quality of internal audit work. Quantitative and qualitative evaluations were conducted, including a logistics regression model and other analyses, using SPSS software. Through semi-structured in-depth interviews and an online survey, 144 responses were obtained from internal Vietnamese auditors of nonfinancial companies listed on the Vietnamese stock market in 2021. After processing the data, the results revealed two factors (independence of internal auditor and management support for internal audit) with a positive influence on internal audit effectiveness, whereas the competence of internal auditors and quality of internal audit work did not affect internal audit effectiveness.