In Financial markets information is in the form of signs, news and different predictions coming from inside or outside of the company which makes reactions and as a result changes in stock prices. Such as increase and decrease over the limit or long period of times. However, this behavior is non-rational behavior of market which can be a rational response to perceived uncertainty that is understood by investors. We investigate the stock market short –term overreaction. The Aim of this project is to analyze overreaction of investors to news and information includes Earnings announcement (Pleasant or unpleasant) in Bear and Bull Market in Tehran Stock exchange (TSE) Using daily data over the period 2005-2011 . Over the window of 14 days before and 14 days after news announcements. The result indicates that investors in Tehran Stock exchange did not have over reaction to information in short time period.