關鍵字:事件宣告、異常交易量、累積異常報酬、資訊不對稱 This study aims to investigate the effects of scheduled events such as dividends declared and earnings announcement, and unscheduled events such as treasury shares and mergers and acquisitions, on the relationship between cumulative abnormal returns and abnormal trading volume. The analysis is based on the intraday order-book data and trading data provided by the Taiwan Stock Exchange between 2005 and 2010. The empirical results show that, before we consider the probability of informed trading, there are no significant relationship between cumulative abnormal returns and abnormal trading volume. However, the two scheduled events had significant effects on the cumulative abnormal returns after we consider the probability of informed trading. The cumulative abnormal returns of high probability of informed trading group during the pre-event period are significantly higher, indicating that there is information asymmetry. On the other hand, the effects of unscheduled events on the cumulative abnormal returns and abnormal trading volume are not significant, even when we consider the probability of informed trading. This result shows that there is no information asymmetry on the unscheduled events. The major contribution of the present research is to analyze the effects of scheduled and unscheduled events on cumulative abnormal returns and abnormal trading volume. The results lead to the conclusion that information asymmetry does exist for scheduled events.