企業在進行擴充規模或是進入一個新的市場時，往往會採取併購的方式來達到目的，在現有的文獻中，對併購的績效已多有探討，研究的重心也慢慢轉為併購完成後的績效。在影響併購後績效的因素中，多數的文獻都將產業相關性作為考量的因素，但其結果卻大不相同。故本研究主要的目的為檢驗產業相關性與併購後公司價值之間的關係，也藉此檢驗主併公司在進行併購後是否有超額報酬。
本篇研究擷取SDC資料庫1995年到2009年併購事件，並以COMPUSTST和CRSP資料庫抓取主併公司的市場報酬及財務資料，最終樣本為3016個有效併購事件，其中包含了1732 個相關併購 和 1284個非相關併購事件。之後利用超額報酬分析檢視相關與非相關併購兩群組之間超額報酬的差異，再以市場報酬為依變數進行迴歸分析，探討控制了影響併購績效的因素後，產業相關性對主併公司報酬的影響。
實證結果顯示，在超額報酬分析中，我們可以發現在相關併購和非相關併購，主併公司併購完成後三年內的超額報酬均為負數，但相關併購的超額報酬有顯著的優於非相關併購;在回歸分析中，我們可以發現，產業相關性與主併公司併購完成後的市場報酬有顯著的正相關。以上兩個方法的結果都顯示產業相關性與公司績效有顯著的相關。

When companies need to expand their business or enter the potential market, they enhance the economic scale and keep the competitive strength by M&A. Under the relevant theories, scholars have increasingly begun to focus on the post-merger performance. Among factors affecting the post-merger performance, most studies take industry commonality into account. There is no consistent conclusion between the industry commonality and performance. The purpose of this paper is to identify the relationship between industry commonality and post-merger performance and further examine whether the acquiring firm has the abnormal return after merger.
The sample of this paper is from SDC during the period 1995 to 2009 and COMPUSTAT and CRSP to acquire the monthly return and financial information. The final sample is 3016 observations consisting of 1732 related and 1284 unrelated acquisitions. We use the measure of abnormal return to examine the difference of abnormal returns between related and unrelated acquisitions. Then, we run the regression and control some factors to discuss the relation between industry commonality and post-merger performance.
In our analysis, the abnormal returns of acquisitions during three years are negative, but the abnormal return of related acquisitions is significantly better than unrelated acquisitions. The related acquisitions have significantly positive relation with market performance in the second and third years.

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