在許多市場異常反應的研究之中，股票買回(stock repurchase)是十分熱門之主題。根據Vermaelen(1981)及Dann(1981)指出，公司宣告股票買回的行為可對投資人發射股價被低估之訊號，間接達到抬升股價之效果。此訊號時常導致投資人開始不理性的買入公司股票，導致公司股價產生異常報酬。然而，當公司實際執行股票買回計畫後，實際執行率卻往往不如公司一開始的預期，使投資人開始對公司發射之訊號開始產生懷疑。
因此，本研究以事件研究法，將股票買回計畫實際執行迄日作為事件日，累積異常報酬做為應變數，自變數則為公司股票買回計畫之實際執行率及其他變數如過去執行率、董監事質押率、市場指數報酬率及買回目的等變數，檢定其對於公司在實際執行迄日後後續股價波動之關聯性。
本文的結論可列為以下幾點: 一、實際執行率與累積異常報酬呈正相關；二、董監事質押率與累積異常報酬呈現正相關；三、市場指數報酬率與累積異常報酬呈現正相關；四、公司執行股票買回之目的為轉讓員工時，其對公司股價帶來之超額報酬會大於買回註銷。

In many studies of abnormal market reactions, stock repurchase is always a hot topic. According to Vermaelen(1981) and Dann(1981), the company’s announcement of stock repurchase could signal investors that the company's stock was underpriced, thus it could raise the stock price indirectly. This signal often causes investors to start to buying stock of the company irrationally, resulting in abnormal returns to the company’s stock price. However, when the company start to implement their stock repurchase plan, their actual execution rate was not as they predicted, and it causes investors to doubt the true meaning of signals.
Therefore, this study uses the event study as research method, and set the last day that company implement their stock repurchase plan as event day. Uses cumulative abnormal return(CAR) as dependent variable, and take the actual execution rate, past execution rate, pledge ratio of boards, the market index return rate and the purpose of the stock repurchase plan as independent variable to test the relevance with the volatility of company’s stock price.
The conclusions of this study could listed as follows: First, the actual execution rate is positively correlated with the cumulative abnormal returns； Second, The pledge ratio of boards is also positively correlated with the cumulative abnormal returns； Third, the market index return rate is also positively correlated with the cumulative abnormal returns； Last, when the purpose of the company's stock repurchase is to transfer stock to their employees, the excess return on the company's stock price will be greater than the cancellation of the stock repurchase.

參考文獻
(一) 中文參考文獻
1、 毛治文 (1999)，內部關係人持股比例及其變動與上市公司購回股票買回之關聯性研究。
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(二) 英文部分
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(三) 網路資料
1、 台灣經濟新報資料庫(TEJ)
http://www.tej.com.tw/twsite/TEJ%E8%B3%87%E6%96%99%E5%BA%AB/tabid/164/language/zh-TW/Default.aspx
2、 全國法規資料庫
https://law.moj.gov.tw/
3、 公開資訊觀測站
http://mops.twse.com.tw/mops/web/index