Over a decade now, performance of deposit money banks in Nigeria based on their profitability was not so good, as many listed banks' annual financial reports indicated decline, negative and fluctuated net profit that led some of the banks to being taken over by others. The study examines the moderating effect of board diversity on the relationship between equity financing and firm performance: evidence from listed deposit money banks in Nigeria. The study covered fifteen listed banks as its sample size from 2010-2019. Secondary source of data was adopted, sourcing the data from Nigeria stock exchange fact books for the period. The proxy for the dependent variable was returns on equity while capital investments and retained earnings represented independent variables and the moderating variable for the study was board diversity. The methodology adopted was STATA 13 version, descriptive statistics, random effects estimate and hausman effect to test the hypotheses. The findings showed that, capital investment is positively and statistically significant with ROE and retained earnings showed a positive relationship and significant with ROE under moderator. The overall model results confirmed that, equity financing has significant effect on firm performance of listed deposit money banks in Nigeria. The study recommended that, deposit money banks in Nigeria should embark on stocks floating to existing and potential investors to subscribe to the banks' shares as a means of capital investment funding to finance their businesses, banks should maintain higher rate of undistributed earnings (retained) to serve as internal source of funds generation for business financing as it bears no costs such as taxes and interest on the firm and to formulate a diverse ethnics and experience board members.