我國庫藏股制度於民國八十九年開始實施，當上市櫃公司宣告買回庫藏股後，造成了公司資產的重分配，其股東、債權人等利害關係人會以預期心理來評估自身權益所受到的影響，並將其反應在所要求的必要報酬率上，因此公司對股東所負擔的權益資金成本及對債權人所負擔的負債資金成本都將產生變動。 當公司宣告買回庫藏股後，實證結果顯示：(1)其負債資金成本將上升，而權益資金成本將會下降。(2)預定買回股份佔資本比愈大時，其負債資金成本增加愈多。(3)買回前獲利能力之不同，並未發現其會對宣告買回公司之負債資金成本有顯著影響。(4)依目的三買回將使該公司負債資金成本增加數小於依目的一或目的二買回之負債資金成本增加數、並使權益資金成本減少數大於依目的一或目的二買回之權益資金成本減少數。(5)公司內部人持股比率於宣告前一年淨增加愈多則權益資金成本降低程度愈大。(6)資訊愈對稱的公司其權益資金成本下降的程度愈少。 / Share repurchase system was formally implemented in Taiwan in 2000 , when the TSEC & OTC listed companies announce that they will repurchase shares , it changes the composition of assets held by the firm , revising the ownership proportions of each of their shareholders and interests of each of their creditors. Thus, their cost of equity capital and debt capital may change . When companies announce to repurchase shares , results show that : (1)their cost of debt capital will increase and their cost of equity capital will decrease. (2)the more percentage of shares companies expect to repurchase , the more their cost of debt capital increase. (3)the different profitability before announcement has no significant effect to companies’ cost of debt capital. (4)repurchase in order to conserve companies’ credibility and shareholders’ equity will increase less cost of debt capital and decrease more cost of equity capital than that in order to reach other two purposes .(5) the more increase of percentage of shares companies’ insiders’ hold before announce, the more their cost of equity capital decrease. (6) the more symmetrical information companies obtain , the less their cost of equity capital decrease.