This very research work has been designed to study investigative “the role which internal audit play in public organization with special reference to post primary school management board (PPSMB) ministry: of university of Nigeria Enugu Campus Board of Internal revenue, sub-treasury as a case studies. However, certain features are very common to the internal audit of all organization as this project is based on the role of internal audit in government establishments. It is therefore divided chronologically into chapters for ease of absorption. Chapter one focus on the research introduction, research background, profile of department used in the case study, its objectives, significance and limitation and research hypothesis. Chapter two deals extensively on the literature review, while chapter three deals on research design and methodology, chapter four concentrate on how the data collected were presented and analyzed. Finally, chapter five contains the summary, recommendation and conclusion based on the findings for an effective internal audit.