We have entered the era of the global village with evolution of science and technology and progress of communication. In recent years, enterprises concentrate on the success and failure of Mergers and Acquisitions (M&A). In terms of operating performance, some operating performance of enterprises were better after Mergers and Acquisitions because it produced synergies. However, some did not turn out well. The main purpose of this study is discussing both the years of mergers and the scale of mergers. Whether the operating performance of group’s enterprises have improved with the increase in the years of mergers and the scale of mergers after M&A has taken place. This study was a quantitative research. The target research is to analyse the M&A activity between the year 2012 and 2014 of listed companies in Taiwan. All sample data of research were taken from the Taiwan Economic Journal (TEJ). The result of research indicated that the years of mergers were positively relevant to operating performance. Earnings Per Share (EPS) had grown significantly up as the years of mergers increased. Return on Assets (ROA) and Operating Profit Ratio (OPR) did not grow significantly up as the years of mergers increased. In terms of the scale of enterprises that was expanded by mergers and acquisitions of enterprises. Earnings Per Share (EPS), Return on Assets (ROA) and Operating Profit Ratio (OPR) had all shown obvious growth as to the opposite scale of enterprises expanded.
