This study investigates the effects of mergers and acquisitions (M & A) on the operating performance of the acquirer banks in Pakistan. For this purpose, a sample of 18 transactions, involving acquirer banks, listed on the Karachi Stock Exchange, is used. The Financial Ratio Analysis (FRA) is used to determine the effects of M & A. The significance of change in the operating performances is tested through a paired sample t-test. The results indicate deterioration in the performances of the acquirer banks in the post-merger period.