One of the fundamental criteria concerning effective decision-making in the stock exchange is stock return which, on its own, possesses an information content that has been used by investors to analyze and predict financial problems. Different studies indicate that shares return will be affected by many variables, one of which is the competitive power of the product market. This study is carried out to find out the effect of the power of the product market competition on stock return of the companies accepted in the Tehran Stock Exchange.The standards of the product market competition are comprised of industry centralization index, goods replacement ability, market size, Tobins Q index, and entrance obstacles (investment intensity). In this study, a sample of 87 companies on the period of 1382 to 1392 has been selected. Considering significant meaning and relation among the presented indexes, the findings suggest that there is a significantly negative relation between industry centralization index, substitute goods capability, market size, Tobins Q index, and shares return of the firms accepted in the Tehran stock exchange. On the other hand, there is no significant relation between entrance obstacles and stock return. The results of analyses indicate that companies with high competitive power have low efficiency.