One of the primary concerns on stock market is the risk associated with securities. There are different attempts devoted to detect and reduce any existing risk and provide necessary action to reduce them as much as possible. In this paper, we study the relationship between quality of earnings and systematic risk as well as cost of capital. The proposed study of this paper uses the information of 150 firms listed on Tehran Stock Exchange and using multiple regression technique examines two hypotheses based on yearly information over the period 2006-2010. The results of our survey indicate that as the quality of earnings increase, the risk as well as the cost of capital decrease.