自台灣實施庫藏股制度以來，許多公司陸續宣告股票買回，然而關於公司經理人對於買回宣告及執行宣告是否具雙重擇時能力，以及市場對執行率的重視程度方面，卻乏人研究。本研究旨在探討上市與上櫃公司宣告股票買回後之實際執行情形以及對執行期間前後股價超常報酬之影響，以期觀察出台灣經理人是否具雙重擇時能力，與投資人對公司進行實際執行股票買回所抱持之態度。經平均數檢定與多元迴歸模型分析，顯示經理人的確同時具有宣告買回及實際執行買回的擇時能力：1.公司宣告股票買回後，不論上市或上櫃公司，股價皆有正向反應；2.執行期間之股價反應與執行率呈反向關係3.執行率與執行宣告後之股價反應呈反向關係；4.執行期間結束後，早實際執行公司之股價反應較晚實際執行公司為佳。本研究結果可供實務上公司實施股票買回的決策參考，同時亦建議主管機關評估庫藏股制度實施成效時，可從公司治理層面中，將公司策略性買回行為納入評估依據。

　　Share repurchases have gradually become firms' important economic activities after the stock repurchase deregulation in Taiwan in 2000. However, few researchers have explored the influence of completion rates on the stock market, and whether managers have dual timing abilities for both repurchase announcements and actual repurchases. This study investigates the market reactions to actual repurchase activities, and managerial timing abilities. Through the t-test and the regression analysis, the results are as follows: 1.Repurchase programs have significantly positive influences on stock prices both to the listed and the OTC firms after the share repurchase announcements; 2.Abnormal returns during the repurchase period are negatively related to completion rates; 3.Completion rates are negatively associated with abnormal returns after the actual repurchase announcements; 4.The abnormal returns of firms that do actual repurchases early are higher than those of firms that do actual repurchases late after the completion period. These results can provide information about managerial decision making in practice, and suggest legislators take firms' strategic trading behavior into consideration while assessing the effects of the legislation about share repurchases.