Abstract :
Merger and acquisition events can influence market depend on the existence of the content of informations in the merger and acquisition phenomenon or not. If the merger and acquisition contain informations then market will react. Objective of this study is to find out the difference of return, abnormal return, trade volume activity, before and, after the merger and acquisition announcement. Research sample is determined by the purposive sampling method, and there are 34 companies which announce merger andAcquisition between 2000-2012. Statistical experiment used is paired samples t test. The observation was done in 11 day, consist of 5 day before, 1 day in the moment, and 5 day after the merger and acquisition. Results of this research show that there is no significant difference between return in period of the moment before and after merger and acquisition announcement. In the case of abnormal return, there is no signification difference in the before and after periode. The activity of stock?s trade volume show there is signification difference in the before and after periods. Cumulatively, it is concluded that merger and acquisition has informed before officialy time. Keywords: Merger , acquisition, return, abnormal return, TVA.