To improve in understanding audit quality, multiple researches were performed to obtain a better understanding for this concept to determine the relationship between audit quality and other variables. One of the variables which its relationship with audit quality was reviewed in many research, is auditor size. One of the first researches in this respect was performed by De Angelo in 1981. In his studies, he concluded that there is a positive relationship between audit quality and auditor size .In the present research, the researchers seek to study the relationship between audit quality and auditor size in Iran. In this study, Iranian certified public audit firms as small audits and audit organization, due to having many personnel and oldness, is considered the big audit. To study the quality, researchers, criterion, the comparison of discovered and reported misstatements in audit reports are performed by separating it into five kinds of misstatements by comparing the current year audit report and statement of retained earning in the future year. The method used is dichotomy research and the statistical analyses performed in this research indicate a meaningful and inverse relationship between audit quality and auditor size.