Stock buy back is the company activities to stock buy back that have been circulating in public. The purpose of the companies do stock buy back is to reduce the ammount of outstanding stock, so it expected to increase the stock price in the market. The stock buy back announcement very important to investors in decision making investment to get maximum income. The purpose of this research is to analyze the difference trading volume activity and abnormal return before and after of stock buy back announcement in 2012-2014. This research is quantitative research with a event study approach. Sample used as many as 33 listed companies on IDX. Data analysis used is descriptive analysis, difference test Paired Sample T-Test, and difference test Wilcoxon Signed Rank Test with a significance level of 0,05. The research results show there has been increasing average trading volume activity and average abnormal return after of stock buy back announcement. It shows that information of stock buy back announcement responded positively by investors. So, can be concluded that there are differences trading volume activity and abnormal return before and after of stock buy back announcement.