Share repurchase is the buyback process that firms use to repurchase their own stocks. It is a major financial policy of many firms, and its use has recently increased. Share repurchases can signal firm value to investors, not only because most firms mention undervaluation as a key motivation for share repurchases but also because investors look favorably on repurchasing decisions. However, it is unclear whether repurchasing firms truly are undervalued. Ikenberry, Lakonishok, and Vermaelen (1995) divided US stocks into two groups based on their book-to-market ratio (B/M), and analyzed each group's long-term stock returns. They found that value stocks with a higher B/M had earned a cumulative abnormal return (CAR) of 45.3% four years after the repurchase announcement, whereas glamor stocks with a lower B/M had earned almost 0% CAR. They concluded that share repurchases are a major signal for value stocks but not for glamor stocks. Byun (2004) divided a sample of firms into two groups based on abnormal earnings before interest and tax (EBIT), and compared low EBIT firms with high EBIT firms. Compared with the high EBIT firms, the low EBIT firms had a negative long-term stock performance, suggesting that undervaluation is not the motivation for share repurchase. How, then, can we identify which of there purchasing firms are truly undervalued? One way to identify undervalued repurchasing firms is to consider insider trading before share repurchase announcements. While share repurchasing is the buyback of a firm's own stocks at the firm level, insider trading is personal trading by individuals with inside knowledge, such as the largest shareholders and directors. The decision-makers for these two types of trading are the same, so insiders have an incentive to increase their personal stakes if the firm is truly undervalued (Lee, Mikkelson, and Partch, 1992; Chan, Ikenberry, Lee, and Wang, 2012). Therefore, we examined whether insider trading prior to share repurchase was an additional signal of firm value. Share repurchasing firms in the KOSPI and KOSAQ markets in Korea were divided into a net-buy group and a non-buy group, based on insider trading for the six months before the repurchases. We then looked for differences between the short-term and long-term abnormal returns of the two groups. We further divided the sample into a value stock group and a glamor stock group, and investigated the relationship between insider trading and long-term abnormal returns. The main results were as follows. First, there were no differences in the short-term abnormal returns of the KOSPI and KOSDAQ markets. There were also no significant differences in the short-term CARs of the net-buy group and the non-buy group, even though the short-term CARs were significantly positive around the time of the repurchase announcements. Firms are required to complete repurchases of their own stocks within three months. It is thus possible that investors do not consider insider trading prior to share repurchase and simply react to the share repurchasing announcement. Second, unlike the short-term reaction, there were significant differences in the long-term abnormal returns of the KOSPI and KOSDAQ markets. There were no significant differences between the net-buy and the non-buy groups in the KOSPI market but there were significant differences between the two groups in the KOSDAQ market. We tested for robustness using buy and hold abnormal returns (BHARs) and CARs based on the Fama and French (1993) three-factor model. We conclude that insider trading can convey additional information regarding firm value only in the KOSDAQ market, which has higher information asymmetry. Third, there were no significant differences in the long-term abnormal returns of value stocks for the insider net-buy and non-buy groups in both the KOSPI and the KOSDAQ markets. However, for glamor stocks, share repurchases by the insider net-buy group showed a larger long-run CAR than those of the non-buy group in both markets. Therefore, we conclude that insider trading prior to share repurchase can convey information, especially for glamor stocks. Overall, insider trading prior to share repurchase is associated with private information about firm value, and can convey a signal in addition to the information signaled by share repurchases.