Abstract
The purpose of this paper is to examine the relationship between product market structure and earnings quality in listed companies of Tehran Stock Exchange. To achieve this goal, we used Herfindahl - Hirschman Index, Lerner and Adjusted Lerner Indexes to measure product market structure and discretionary accruals for earnings quality. Our sample consists of 1144 out of 143 observations of firms for the period of 2008-2012. Using Panel Data Method, we found a significant positive relationship Herfindahl -Hirschman Index and earnings quality. Furthermore, the results show a significant positive relationship between the Lerner Index and the Adjusted Lerner Index and earnings quality. This finding means that no matter how the competition is more in the industry; the earnings quality will be higher.