金融業實務中，購併行動愈來愈普遍。尤其金控公司經常採行水平購併以進行業務多角化經營。但是，實際上相當多的購併行動並未成功地帶來財務績效提升，因此影響購併後財務績效之相關學術研究愈來愈重要。本研究運用台灣金融控股公司資料，探討購併後多角化對財務績效之影響。本研究建立模型，探討金控公司購併後，業務多角化分別經由中介變數：成本及市場相關表現對財務績效之影響。本研究四項實證結論分別為：(1) 多角化對變動成本率有顯著正向影響，因此降低財務績效。(2) 多角化對市場相關表現有顯著負向影響，因此降低財務績效。(3) 經由市場相關表現對財務績效的影響，大於經由成本率對財務績效的影響。(4) 市場相關表現與變動成本率呈顯著正相關。

Mergers and Acquisitions (M&A) have become increasingly popular in the banking industry, and especially the horizontal M&A of financial holding companies done for diversification. However, there is considerable evidence that many M&A are unsuccessful. Thus, studying factors that influence the result of diversification after M&A is a promising field for academic research. This paper investigates the impact of diversification after mergers and acquisitions on the performance of financial holding companies, using a sample of financial holding companies in Taiwan. A model is postulated in which diversification can influence financial performance through the two variables of cost and market-related performance. We generate four empirical generalizations. (1) Diversification is significantly positively associated with variable cost, thus reducing financial performance. (2) Diversification is significantly negatively associated with market-related performance, thus reducing financial performance. (3) The effects on market-related performance are greater than the effects on variable cost. (4) There is a significant positive relation between marketrelated performance and variable cost.