It is thought that there is a strong relationship between the key audit matters and internal control structures of enterprises. The purpose of the study is to reveal whether this relationship differs in sectoral terms. For this; sectoral comparison of key audit matters and possible deficiencies in internal control impacting on key audit matters, determining the COSO principles which are considered not to be effectively implemented by the enterprises in the emergence of the relevant deficiencies, have been determined as sub-objectives. In the scope of the research; the audit reports of 45 companies traded in Borsa İstanbul A.Ş., including energy, food, automotive, construction and tourism sectors, for 2017, 2018, 2019 were analyzed using content analysis, one of the qualitative data analysis methods. As a result, it has been determined that there is a strong relationship between the internal control systems of the enterprises and key audit matters and that there are differences depending on the structural characteristics of the sectors. And also; it has been determined that deficiencies in internal control, which are expressed as incorrect / incomplete data use, incompetent personnel and lack of systematic process control and evaluation, are common across sectors. It has been concluded that the COSO principle regarding the assessment of fraud risks is the most important principle that cannot be effectively implemented by businesses.