This research objective is to analyze the influence of ex-dividend date announcement in the Jakarta Stock Exchange by taking 14 samples of shares. There are two kinds of samples, increasing dividend and decreasing divindend. 120-days of observation will be divided into 90-days estimation period and 30-days event period, including 15 days before and after the event. The method used in this research is event study that observe the stock price movement in the capital market. To examine the existence of price reaction, the abnormal return test will be conducted during the event period with analysis based on the concpet of CAPM (Capital Assets Pricing Model) and the abnormal return test to the increasing and decreasing dividend at the ex-dividend date. The result indicate that at the significant level of 10%, there are two working days which yield the abnormal return that is significant at the increasing dividend. Those are the fourth day before the event date with the value of 0.0011102 or around 0.1%, and the fifth day after the event date with the value of -0.32184 or approximately 3%. Whereas the decreasing divideng reveals that there are three days that deliver the abnormal return which is significant. Those are thirteentg and the second day before the event date with the value of 0.028263 or approximately 2% and 0.0166274 or approximately 1%, as well as at the fifth day after the event date with the value of 0.029105 or 3%. The final conclusion is that stock price will negatively reacted to the announcement of increasing dividend at the ex-dividend date and positively reacted to the announcement of the decreasing dividend at the ex-dividend date.