This study examined the effect of merger and acquisition on deposit money banks’ performance in Nigeria. The objectives were to determine the level of deposit money banks’ profitability, customer deposits, total assets and shareholders capital in pre-merger and acquisition era and post- merger and acquisition. This was done to find out if there had been any meaningful development in the banking sector since merger and acquisition programmes of the Central Bank of Nigeria (CBN). This study employed an ex-post facto research design since researcher cannot manipulate the independent variables. Time series data were collected from CBN and NDIC Report in the Nigerian banking industry using the time frame of 1992 to 2021. The test of difference of means method was adopted. Findings showed that there is significant difference in the profitability, customer deposits, and shareholders fund of deposit money banks in the pre-merger and acquisition and post-merger and acquisition. However, there is no significant difference in their total assets. It recommended that the merger and acquisitions policy be reviewed at various periods since it enhances the profitability of deposit money banks in Nigeria.