The regulation of the RI Ministry of Industry regarding Low Cost Green Car (LCGC) is a reference for the automotive companies that manufacture vehicle segment and it becomes information to stock market participants. The purpose of this study is to determine the differences of the stock market reactions towards the announcement of the aforesaid regulation against the abnormal return and trading volume activities. It uses event study approach by observing the abnormal return and trading volume within 60 days period before and after the announcement of the regulation where PT Astra International Tbk and PT Indomobil Sukses International play as samples. Result indicates that there is no significant difference in the abnormal returns of the two companies. However, there is a significant trading volume activities within determined period.