Business combination through mergers and acquisitions has become a global phenomenon to achieve economies of scale and higher productivity. The need for financial institutions to merge becomes even more imperative in the face of the onslaught of greater competition arising from globalization. This study evaluated the impact of mergers and acquisitions which started in 2005 on the performance of deposit money banks in Nigeria using a sample of ten (10) banks. This research made use of secondary data, obtained from the bank’s annual reports and statements of accounts covering a period of 2001-2010, Using nine (9) variables; Return on Assets, Return on Equity, Net Profit Margin, Asset Utilisation, Equity Multiplier, Earnings per share, Debt Equity ratio, Debt Asset ratio & Leverage ratio, the study evaluated the performance of the banks before and after mergers and acquisitions using pair sample t-test. The results showed that there is significant difference in the performances of Deposit Money Banks in the pre and post-merger periods using the ROA, ROE and LR as yards tick but shows no significant impacts in the performances of Deposit Money Bank using other variables as yard stick. The study hereby recommends that the CBN should set and enforce corporate governance standards for commercial banks and also enforce risk based supervision in banks.