The purpose of this paper is to examine corporate insiders trading strategy from insider filing date in relation to earnings announcement of firms listed in the Stock Exchange of Thailand during 2003 to 2012. Corporate insiders trading activity is measured in term of amount of shares trade, frequency of transactions and value of shares trade before and after earnings announcement. Abnormal returns over earnings announcement day are used as a proxy to market responses to the announcement. By employing event study approach, the results show that corporate insiders in Thailand buy and sell their own firm stock in view of positive market reaction from good news announcement. They also sell and buy their own firm stock in view of negative market reaction from bad news announcement. However, earnings announcement may not be the factor that corporate insiders use in order to make profit from entering or exiting their position on the foreknowledge of earnings information.