This study examines the market’s reaction to disclosures of insider transactions announced by DART system and analyzes the determinants of the stock market reactions to insider trades disclosures. Specifically, we focus on three factors likely to affect informativeness, reporting lag, trade type (purchase versus sales), and informational environment difference between two exchanges (KSE versus KOSDAQ). First, reporting lag is included to capture the potential effect of leakage on the information content of insider trading disclosures as a function of the delay between the transaction and its disclosure dates. If leakage increases with the reporting lag, then the association will be weaker. Second, we include the type of insider trades(sale or purchase) because the market reactions that stem from insider purchases and sales may be asymmetric. By purchasing shares in their firm, insiders communicate a positive signal about the future value of the firm to the market. The signal is costly as the insiders incur a substantial cost to acquire their shares and bear the cost of holding less than optimally diversified investment portfolios. Therefore, insiders’ purchases must stem from confidence of future performance, sending a credible positive signal about a firm’s future financial health. Conversely, insiders signal negative news when selling shares. However, the negative signal may be less informative as liquidity needs, rather than changes in the firm’s future prospects, may force the insiders to sell shares. Finally, we consider stock exchange membership(KSE or KOSDAQ). The market response to insider trading disclosure will depend on the degree of informational asymmetry between insiders and market. In general, informational asymmetry between insiders and market may be stronger in KOSDAQ than KSE. Therefore, investors’ reaction to the public disclosure is expected to be stronger for KOSDAQ firms than KSE firms. We analyze market reactions to a sample of 30,120 insider trades disclosures from 2001 to 2012. Our major findings are as follows. First, we find a significant price reactions to public disclosures of insider trades, which implies that disclosure on insider trading communicates useful information to stock market investors. Second, there is a significantly negative association between market reaction and reporting lag around announcement dates. This result shows that the information content of insider trading disclosures increases with their timeliness. Also, this result suggests that more timely disclosure mandated by the new rule under Financial Investment Services and Capital Markets Act contributes to more efficient stock market. Third, we found that insider purchases mainly induces price reaction whereas insider sales induces trading volume reaction, implying that investors react to insider purchases and insider sales in a different way, respectively. Finally, it is found that the market reaction to public disclosure of insider trades is stronger in KOSDAQ than KSE, which is consistent with the notion that information content of insider trades turns out to be stronger for firms with higher degree of information asymmetry. Most of previous studies investigate the relation between insider trades and stock prices with a focus on the realized abnormal returns obtained through insider trading. In contrast, our study examines the informational effects of public disclosure of insider trades and also their determinants of cross-sectional variation across firms. We are unaware of any research, using Korean stock market data, that investigates public disclosure effects of insiders’ trades. Therefore, our study contributes to literature by showing the benefits of providing investors with more timely information about insiders’ trades.