Diversification can be considered as a form of corporate strategy that managers use to improve company performance. Diversification strategies show a situation in which representation problems between managers and shareholders have been reduced. Reducing agency problems depends on having a group called independent auditors who identify deviations and guide managers to perform better. The purpose of this study is to study the effect of auditor characteristics on the value of corporate diversification. To measure corporate diversification, the entropy index of corporate product diversification and geographical diversification was used. Also, to determine the value of diversification, Fama and French models were used. The characteristics of the auditor were assessed using three criteria: auditor size, auditor industry expertise and auditor tenure. The statistical population of the study includes companies listed on the Tehran Stock Exchange during the years 1391 to 1396. Regression analysis and Spearman correlation test were used to test the hypotheses. The results show that the characteristics of the auditor (auditor size, auditor industry expertise and auditor tenure) do not have a significant effect on the value of corporate and geographical diversification.