The purpose of the study is to identify factors affecting the effectiveness of internal control system in an organisation. Based upon a case study of a public sector undertaking in Tigray, Ethiopia, the paper examines how internal control system’s quality, management support, organisational setting, and the interplay among these factors, influence internal control effectiveness. The findings of the study highlight that internal control effectiveness is strongly influenced by internal control quality and management support, whereas organisational setup also have a strong impact on internal control effectiveness. Study also highlights that there is no proper internal control system in the office of the construction for irrigation in Tigray, Ethiopia and they will have to learn a lot in order of being properly framed managed.