The reported earning quality is very important to users because a low-quality reported earning results in inefficient allocation of resources and damages the interests of investors. Therefore, identifying the factors affecting earnings quality seems essential to improve it. One of the factors that regulatory bodies are always concerned about is the mandatory versus voluntary auditors’ rotation. In this regard, the purpose of the present study is to investigate the impact of short-term and long-term auditor tenure on earnings quality and then to examine such an impact in the presence of information asymmetry. For this purpose, we used the financial information of 103 companies listed in Tehran Stock Exchange during time-period of 2008-2017. We utilised panel regression method for analyzing the data. The results indicate that the long-term auditor tenure has a positive effect on earnings quality, but the Short-term auditor tenure has a negative effect on earnings quality. Supplementary research findings indicate that the long-term auditor tenure in firms with a higher level of information asymmetry results in greater earnings quality, but the short-term auditor tenure in such firms results in a greater reduction in earnings quality. The findings of the study provide evidence in supporting the auditor's expertise hypothesis against the auditor’s independence hypothesis.