Abstract: This study aims to determine whether there is a significant impact of Tax Amnesty announcement on July 1st 2016 toward Indonesia Stock Exchange (IDX) period of February – July 2016. The research conducted event study method to examine the phenomenon. Event studies aim to examine abnormal rates of return by the significant economic information. Sample of the research was 78 companies that listed on KOMPAS-100 index which are not doing any corporate action during event window of 5-days before (t-5) until 5-days after event date. Average abnormal return was being variable of the research by calculate market model with 100-days of estimation date. The research concluded that there is no significant difference in event window of 5-days before and 5-days after Tax Amnesty announcement.