The present study examines the impact of Concentration on Customer on earnings management in terms of the presence of major customers in the company. Suppliers with major customers will need to hold higher cash inflows because of the high risk of losing major customers. Companies can increase their cash flows through various instruments such as debt issuance and external financing, non-payment of dividends, and manipulation of earnings items. The results obtained in this study confirm these statements. In the context of the empirical test, 140 of the selected companies were screened using the Tehran Stock Exchange during the period from 2011 to 2016. To test the hypothesis of the research, has been used multiple regression model using combination data. The results supported of the negative impact of Concentration on Customer on accruals earnings management. Also, the results showed that Concentration on Customer on real earnings management had a negative effect. The present research can lead to a more accurate understanding of the role of the major customers of the company in earnings management and show how Concentration on major Customer affects corporate earnings management.