A Dissertation Submitted in Partial Fulfilment of the Requirements for Award oftheDegree of Master of Science in Accountancy and Finance (MSc A& F) of Mzumbe UniversityIn order to succeed an organisation need to have good corporate governance. Internal audit functions as a service to management can ensure this by being effective. The main aim of this study was to examine the effectiveness of the internal audit function as a corporate governance mechanism in the public sector in Tanzania with special focus on the office of the Internal Auditor General’s Division (IAGD).The study specifically endeavoured to determine the status of internal audit as a corporate governance tool in Tanzania, to determine internal audit good practices ensuring sound corporate governance and identifying factors that affect directly the effectiveness of the internal audit function in the Tanzanian public sector. The study employed a case study technique. Purposive sampling was used to collect data from all the internal auditors in the offices of IAGD. Out of a total of 34 respondents, a total of 28 (82.35%) responded. This study employed both primary and secondary information. The results from the analysis concluded that the effectiveness of the internal audit function as a corporate governance mechanism in the public sector in Tanzania is brought about by all the examined factors except segregation of duties. Also, it was found that effectiveness of internal audit function had led to good corporate governance at IAGD. Recommendations were made to both the central government and IAGD. The central government was advised to review the structure, nature of appointment and recruitment process, overlap of functions, nature of distribution of tasks and responsibilities, and the number of employees in IAGD. Also, the management of Internal Auditor General’s Division were advised to make sure audit recommendations are implemented by audited entities and provide its employees with all support needed.