股票買回已逐漸成為公司一種重要的經濟活動，自台灣實施庫藏股制度以來，許多公司陸續宣告股票買回，然對於公司是否實際執行股票買回，以及是否可利用不實際執行就使股價攀升的問題，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，對執行期間前後股價超常報酬之影響，以期看出台灣經理人是否有擇時能力，與投資人對公司進行實際執行所抱持之態度。研究期間為民國89年10月16日開始，至民國94年11月15日止，共選取1147件上市公司，445件上櫃公司股票買回宣告為研究樣本。經由平均數檢定與多元迴歸模型分析後，研究結果如下：1.公司宣告股票買回後，無論是上市及上櫃公司，股價皆會有一段時間的正向反應。2.執行期間之股價反應與執行率呈反向關係。3.執行率高低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. Many firms announce share repurchases since “Regulations Governing Share Repurchase by Listed and OTC Companies” were deregulated in Taiwan in 2000. However, only few researchers examine completion rates and whether firms can make profit but do not repurchase actually. This paper investigates the actual repurchase activity and its stock price reaction, to see the market reactions toward the actual share repurchases and managerial timing abilities. The research period begins from October 16, 2000 to November 15, 2005, contains 1147 listed firms and 445 OTC firms. Through the t-test and the regression model, the results are as follows: 1. It is found that repurchase programs have significantly positive influences on stock price both to the listed and OTC firms after the share repurchases announcement. 2. Significantly negative relations between abnormal returns and completion rates are examined during the repurchase period. 3. Significantly negative relation between abnormal returns and completion rates are examined after the actual repurchase announcement. 4. The abnormal returns of firms that do actual repurchases early are higher then those do actual repurchases late after the completion period. The result 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 repurchase.

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