本研究旨在探討台灣地區實行庫藏股制度初期，上市公司初次宣告購回庫藏股之股價反應，並以事件研究法檢視不同產業及不同購回目的之庫藏股購回宣告效應之差異，以及探討購回庫藏股比例、內部關係人持股比率、內部關係人淨買入比率、公司規模及淨值/市價比等因素與累積異常報酬之間的關連性。實證結果發現：公司宣告庫藏股購回對股價有正向之資訊內涵。整體而言，以維護股東權益與公司信用為申報目的之樣本公司，其累積平均異常報酬率顯著大於以股權轉換為申報目的之公司；非電子業庫藏股購回之正向資訊內涵較電子業之反應強；淨值/市價比及庫藏股購回之比率與累積異常報酬間成顯著正相關，公司規模與累積異常報酬間成顯著的反向關係，而內部關係人持股比率及內部關係人淨買入比率則對累積異常報酬無顯著影響。

This study investigates stock price responses to open market stock repurchase in Taiwan. We test the difference in announcement effect between electronic and non- electronic industries, and the difference in announcement effect between different announced purposes of stock repurchase. Event study is employed to measure abnormal return around the announcement. The factors, including the repurchase amount, insider holdings, insider net buying, firm size and book-to-market ratio, are examined. Results show that the stock repurchase announcement has a positíve effect on stock price. We also find that there are significantly different responses between the electronic and non-electronic industries, and different announced purposes of stock repurchase. Furthermore, the accumulative abnormal return is positively related to book-to-market ratio and repurchase amount, and negatively related to firm size. However, the results show that the accumulative abnormal return is not related to insider holdings and insider net buying.