庫藏股制度於國外已經行之有年，特別是美國，早在1960年代即有庫藏股交易。我國上市上櫃股票可合法買回自己公司股票制度始於2000年所通過的上市上櫃公司買回本公司股份辦法，除了希望藉以提振東南亞金融危機中不振的股市表現，也賦予企業多一種能向投資人傳遞訊息的管道。本研究基於股票買回的各項假說，希望探究公司股票買回宣告的動機還有事件宣告後對於公司股價的影響效果，最後並檢視公司的宣告決策是否會受到前次購回宣告的表現所影響。 在假說驗證方面，以2000至2004年上市公司832家、上櫃公司236家曾經宣告買回自家股票的公司為研究樣本，輔以選出與買回樣本同時間的相同數量「未買回樣本」，透過1-way ANOVA測試與鑑別分析探討影響公司宣告股票買回的因素符合哪些假說的推論結果。此外，依據各項假說，進ㄧ步利用1-way ANOVA測試和複迴歸分析找出與公司事件宣告後股價異常報酬率之間的關係，接著以1-way ANOVA檢視最後一部份研究主題。經由上述的實證分析，本研究獲得以下主要結論： 1.公司買回自家的股票平均而言對於股價有正面的影響效果。 2.以上市公司而言，影響公司宣告股票買回的假說包括了：自由現金流量假說、個人所得稅節稅假說與財務槓桿假說。以上櫃公司而言則包括：自由現金流量假說、個人所得稅節稅假說與資訊信號假說。 3.以上市公司而言，股票買回宣告後，股價的正向異常報酬與：自由現金流量假說、管理者的誘因假說呈現相關關係。上櫃公司則包括：自由現金流量假說。 4.本次是否再度宣告股票買回會受前次買回的正向累積異常報酬率所影響。 / Stock price reactions on stock repurchase announcements among publicly traded corporations have been widely studied over 40 years in United States. Several hypothesizes were established and provide logical reasons for why corporations buy back their own stocks. References show large proportion of positive effect on post-announcement stock price after stock repurchase announcements from empirical researches. It is since 2000 that corporations are allowed to repurchase their own stocks legally in Taiwan. Although many efforts were put in surveying the post-announcement stock price reactions, few focused on examining how corporations’ repurchase decision would be influenced by different hypothesizes. Moreover, whether or not previous repurchase outcome may affect future repurchase judgments met contradict conclusion from recent studies. This research aims on exploring the two main topics which form 7 hypothesize. Data collecting from Taiwan Economic Journal (TEJ) database, Commercial Times and Economic Daily News contains publicly traded corporations had ever made stock repurchase announcement except financial and government institutions. The period of the study was from Aug. 6, 2000 to Jul. 31, 2004 and total number of announced corporations included was 832 listed on the Taiwan Security Exchange with 236 listed on the OTC separately. Hypothesis 1 to 6 were tested both from individual model using 1-way ANOVA Analysis and integrated model using Discriminate Analysis on Hypothesis 1 to 5, Event Study Analysis on Hypothesis 6. Hypothesis 7 was also verified with 1-way ANOVA Analysis. The empirical results show supports in several hypothesize which reflect corporations did concern free cash flow amount, leverage level, stock underpriced and dividend payout level issues when making repurchase announcement. The stock price after announcement has certain degree of moving correlation toward the same direction as free cash flow level and managerial stockholding level. Finally, previous repurchase outcome was found holding opposite relation with future repurchase judgments.