As competition in the profession grows, audit firms have increasingly recognized the need to provide better quality services and lower costs to the market. Audit firms seek to optimize their costs and offer the best value for money, not only to maximize their income but also to lose their job in competitive conditions. Factors affecting the audit fee can be very useful, given the specific turbulence in the audit labor market, there is no clear basis for determining the auditor's cost, and sometimes auditors' judgments lead to inconsistent proposals. . The present study investigates the relationship between firm characteristics and auditor fees. In this study, data of 201 companies in Tehran Stock Exchange during the period 2012-2012 were used. Regression model and Eviews software were used for data analysis and hypothesis testing. The results show that there is a positive significant relationship between accounting complexity and audit fee and there is a positive and significant relationship between business complexity and audit fee.