Aalia Ghinannafsi Musdhalifa, Mergers and Acquisitions on Stock Market Reaction: Evidence from Indonesia, Under Mr. Burhanuddin, SE., M.Sc as advisor. This study aims to see stock price reaction, before and after mergers and acquisitions. This study examined events related to the impact of merger and acquisition announcement on abnormal return companies that go public and listed on the IDX through 2014 to 2018 by using event study. The sample consisted 5 companies listed on IDX. Specified the event study by applied an event window of 41 days of stock that actively traded including 30 days of estimation period, 5 days prior to, 1 day as an announcement, then followed by 5 days after mergers and acquisitions. Used One Sample t-Test and One Sample Wilcoxon Signed Rank Test to see significant changes in daily stock price during observation period then used Paired Sample t-Test to determine whether there is any differences abnormal return prior to and after events. The result shown that there are several significant changes in daily stock price through observation period, while there is no differences in abnormal returns prior to and after announcement of mergers and acquisitions for companies listed on IDX from 2014 to 2018.