This study examined the effect of non-performing loans (substandard loans, doubtful loans and loan loss) on financial performance (Return on Assets-ROA) of listed Deposit Money Banks (DMBs) in Nigeria. Ex-post facto research design was adopted for the study. The study has the population of fifteen (15) banks listed on Nigerian Exchange Group as at 2021 where Thirteen (13) listed DMBs were selected. Secondary data was extracted and used from the annual reports and accounts of the sampled banks for the period 2012 to 2021.Data were analyzed using descriptive statistics which provides the description of the data, correlation analysis which provided the relationship between the dependent and independents variable, it also show the relationship between the independent variables among themselves and regression analysis used to test the formulated hypotheses. The study found that substandard loans has positive insignificant effect on financial performance of deposit money bank in Nigeria. While doubtful loans have a negative significant effect on financial performance of deposit money banks in Nigeria. However, loan loss has a significant positive effect on financial performance of deposit money banks in Nigeria. The study concluded that non-performing loans has effect on financial performance of DMBs in Nigeria. The study therefore recommends the management of the deposit money banks in Nigeria should design and maintain a robust credit management strategy & framework as well as stringent credit policy that would decrease non-performing loan and default level; and improve their performance level.