本研究的併購動機主要分為綜效假說、代理假說和傲慢假說。我們以目標公司報酬和總報酬的相關性，以及目標公司報酬和主併公司報酬的相關性來區分此三種假說。併購動機若支持綜效假說，則預期目標公司報酬和總報酬呈正相關，且目標公司報酬也和主併公司報酬呈正相關。併購動機若支持代理假說，則預期目標公司報酬和總報酬呈負相關，且目標公司報酬也和主併公司報酬呈負相關。併購動機若支持傲慢假說，則預期目標公司報酬和總報酬無關，且目標公司報酬和主併公司報酬呈負相關。 　　本研究探討美國88件國內併購案以及79件跨國併購案，樣本期間為2000年1月1日到2006年12月31日。根據本研究的實證結果，做出以下結論： 1、在國內併購案中，併購的動機主要來自綜效假說和傲慢假說。而在跨國併 購案中，併購的動機主要來自代理假說和傲慢假說。 2、沒有足夠的證據顯示以傲慢假說為併購的動機會減少公司的價值。 3、匯率的變動並不影響企業從事跨國併購的動機。 / This paper develops tests to distinguish among the three major motives for M&A：synergy、agency and hubris. We distinguish three hypotheses by observing the correlation between target, acquirer and total gains. If the motive supports the synergy hypothesis, it expects positive correlation between target and total gains. The synergy hypothesis also expects positive correlation between target and acquirer gains. If the motive supports the agency hypothesis, it expects negative correlation between target and total gains. The agency hypothesis also expects negative correlation between target and acquirer gains. If the motive supports the hubris hypothesis, it expects zero correlation between target and total gains. The hubris hypothesis also expects negative correlation between target and acquirer gains. 　　This paper treats 88 domestic and 79 cross-boarder cases of M&A over the period of 2000 to 2006 in America. According to the empirical result of the study, the conclusions are stated as follows： 1. In the domestic cases of M&A, the synergy hypothesis and the hubris hypothesis are the primary motive of M&A. In the cross-boarder cases of M&A, the agency hypothesis and the hubris hypothesis are the primary motive of M&A. 2. It has no adequate proof to show the motive of M&A flows from the hubris hypothesis may decrease the value of the company. 3. The variation of the exchange rate has no effect on the motive of cross-boarder M&A.