ix, 144p. :ill.Corporate governance, as an antidote to corruption, has received significant public and regulators attention in today ‘s global world and the internal audit has been identified as the most effective control mechanism to ensure good corporate governance in the public sector. This study, therefore, investigated into the effectiveness of the internal audit units in the public sector in promoting good corporate governance. It reviewed history of internal audit, corporate governance, internal control and factors that contribute to the effectiveness of internal audit. Descriptive research method was employed. Simple random sampling and census procedures were used to obtain data from 29 internal auditors and 9 branch heads of Ghana Audit Service in the Northern region of Ghana. Statistical tools used were mean and percentage. The study revealed that the internal auditors receive less management support and the audit committees in the assemblies are not effective. It is also evident that majority of the internal auditors did not have requisite skills and experience. The units also experienced inadequate resources allocation. This suggests that the internal audit units in the assemblies are not effective Therefore, to ensure good corporate governance, the internal audit units should have appropriate governance structure, sufficient and appropriate resources and competent personnel.