The study examined the effect of board diligence on financial performance of deposit money banks (DMBs) listed on the Nigerian Stock Exchange. Data of the 10 selected DBMs were obtained from their annual financial statements from 2012 to 2018 using an ex post facto research design and purposive sampling technique. The data were analysed using inferential statistics and the hypothesis was tested using Generalised Method of Moment (GMM). It was found that board diligence has significant negative effect on financial performance of Nigerian listed DBMs. As regards the controlled variables, only capital adequacy and firm size were found to positively and significantly influence financial performance. Liquidity ratio was found to have direct but no significant effect on financial performance while nonperforming loan negatively and insignificantly affect financial performance. The study concludes that board diligence reduces financial performance. It is therefore recommended that preference should be given to the quality of board meetings and not the frequency of such meetings; and that issues that have implications on performance should be given utmost attention at board meetings.