At the end of the nineteenth century, a loss of confidence in financial statements was observed in response to the corporate frauds that took place in many recognized corporations worldwide as Parmalat, Enron, and Worldcom. Corporate governance and internal auditor independence had become two concepts of major concern. The importance of the role of corporate governance in the guarantee of the quality of financial reporting is recognized. Audit committee, external auditors and management ownership are essential components in the corporate governance mosaic that are given high importance in this study and their influence on the effectiveness on internal audit function is deeply illustrated. In order to go beyond the theoretical link between corporate governance and internal auditor effectiveness, this study will illustrate through a survey using a quantitative methodology, the real impact of corporate governance components on internal audit effectiveness in the Lebanese firms. Primary data is collected through a questionnaire filled by auditors, members of audit committees and managers from a sample of selected Lebanese firms. The questionnaire was sent to 50 persons from whom 41 responded. The results originated from our study provide a response to the research question and confirm the hypotheses based on the previous literature. We have concluded that, in Lebanon, qualifications, effectiveness of audit committee and interaction with internal auditors have a positive influence on internal audit effectiveness. In addition to that, we can confirm that communication between internal and external auditors enhance internal audit effectiveness. However, managers holding a high percentage of shares may impair internal auditor independence which constitutes a component of internal audit effectiveness.