Analysis of investors’ behavior is a new scientific field in financial behavior, which is a good tool for acquiring this knowledge. Uncertain circumstances cause investors to make systematic mistakes and face cognitive biases in their expectations and decision making, including in assessing stock returns. The purpose of this study is to investigate the extent to which investors follow the pattern of belief updating as a cognitive bias in the use of earnings accounting information to evaluate the stock returns of 205 active companies in Tehran Stock Exchange. Multivariate regression analysis was performed using Eviews 9 software. The results show that by controlling year and industry effects, investors use profitability for most of the past years in following the pattern of belief updating based on two indicators of reducing realized earnings per share and equity returns. The research model is also confirmed by the sensitivity analysis and controlling company effects based on the equity return index. However, it is not confirmed by the two indicators of realized earnings per share and return on assets.