This article presents the trading behaviours of individual and institutional investors in Korean mergers and acquisitions market. Based on Chen et al. (2007), we consider a bidder's negative abnormal announcement-period return as a measure for bad merger. To investigate the investor trading behaviours around the bad mergers, we employ a unique daily trading data of different groups of investors in Korean stock market. Our finding shows that institutional investors sell their shares on a bidding firm before announcement of a bad merger, while individual investors buy the shares. In addition, we find that institutional investors continue to sell their shares on a bidding firm even after announcement of a bad merger, but individual investors keep buying them. Hence, our results newly support the hypothesis that individual investors are less informed and/or less sophisticated than institutional investors.