Tax collection serves as an important source of revenue for the government of which, can be highly influence by the ability of tax auditors in performing their tasks. This study aims to examine the factors influencing tax audit effectiveness of the tax auditors in the Inland Revenue Department in Malaysia (IRBM). Specifically, this study examines whether audit case selection, supervision monitoring and auditors' characteristics influence tax audit effectiveness in of the tax auditors in the Inland Revenue Department in Malaysia. Using questionnaire survey distributed to tax auditors, this study shows that all the factors chosen in this study namely, audit case selection, supervision monitoring and auditors' characteristics significantly influence tax audit effectiveness among the tax auditors in IRBM. The findings in this study could help tax administrators to monitor IRBM's tax auditors to increase their efficiency. The results are expected to assist IRBM in identifying factors contributing efficiency and competency among IRBM tax auditors. This may enhance further steps and actions to improve level competency among the IRBM's tax auditors to help achieve its aspiration to be the leading tax administrators in the world. It will also help IRBM to consider the suggestion and recommendation in order to produce good and competence tax auditors in the future.