Financial Deepening boosts the income of deposit money banks (DMBs) which in turn enhances the profitability and contribution of such banks to economic growth and development. In the case of Nigeria, this has not been properly situated. The focus of this study is to determine how financial deepening has spurred the income diversification and growth of selected DMBs. Purposive sampling technique was adopted in selecting the DMBs studied. Descriptive Statistics and panel data regression analysis were used in estimating the econometric model for the study. Results showed that financial deepening had significant positive effects on the income of DMBs listed in Nigeria and recommendations include a policy rethink on the part of regulatory authorities by the provision of guidelines that will facilitate more credit to MSMEs and DMBs on their part should diversify their income sources by expanding their non-interest income base.