本研究探討臺灣新股公開上市 (Initial public offerings; IPOs)後，股票強制集保(Lockups)期間 結束後的股價行為。由於實務上內部人在集保期 結束後七天才可以開始出售持股，我們分別檢視 強制集保期結束前一日至後一日之超額報酬，與 強制集保期結束後七日至九日之超額報酬，發現 兩者都是負報酬，後者顯著地異於零。此外，我 們也發現，在集保期結束時的期間，股票的成交 量有顯著地增加。這些實證結果都與近期之文獻 一致，顯示市場缺乏足夠的效率性。最後，實證 結果顯示，集保股票愈多、有創投基金的 IPOs， 在強制集保期結束後的股價下跌幅度較大。 This research examines the stock behaviors around lockup expirations on Taiwanese IPOs. According to the rules of lockup practice, insiders can sell lockup shares beginning the 7th day from the lockup expiration. Therefore, we investigate the abnormal returns not only around the period of lockup expiration, but also around the period of insiders probably first selling their lockup shares. Empirical evidence shows that the abnormal return in both periods is negative, and the latter one is significantly different from zero. Furthermore, we find that the trading volume increases dramatically around the lockup expiration. These results are consistent with the findings of the previous literature, which are against the efficient market hypothesis. Finally, IPOs with a larger fraction of lockup shares and with VC investors experience a larger negative return.