The purpose of this research is studying the effect of Audit firm’ s characteristics on earnings management. Accrual and real earnings management are measured through the models proposed by Dichow & Dichev (2002) and Roychowdhury (2006). Audit firm’ s characteristics consist of age, competition power, independence, number of partners, ranking by Iranian Association of Certified Public Accountants, ranking by Tehran Securities & Exchange, rotation, size, specialization and tenure. Samples include 99 firms listed in Tehran Securities & Exchange. Hypotheses have analyzed using multivariate regression models. Findings indicated that audit firm’ s independence, ranking by Iranian Association of Certified Public Accountants, rotation and size havesignificant effect on accruals earnings management; Audit firm’ s age, competition power and size havesignificant effect on real earnings management through abnormal operational cash flow. Audit firm’ s age, independence, ranking by Iranian Association of Certified Public Accountants, size, specialization and tenure havesignificant effect on real earnings management through abnormal production cost; In addition, audit firm’ s age, competition power, ranking by Tehran Securities & Exchange, size, specialization and tenure havesignificant effect on real earnings management through abnormal discretionary expenditures. However, accruals and real activities earnings management do not affected by the number of partner in audit firms.