The performance of any business firm not only plays the role to improve the market value of that specific firm but also leads towards the growth of the whole sector which ultimately leads towards the overall prosperity of the economy. Assessing the determinants of the performance of organizations has gained importance in the corporate finance literature; however,this study examines the determinants offinancial performance listed mega banks in Nigeria for a period of seven years. The population of this study comprises the 11 listed mega banks in Nigeria as at 31 December, 2013. A total of 8 banks that meet the criteria were duly selected as sample for the study. The audited annual reports (Balance sheet and Profit/Loss account) were obtained from Central Bank of Nigeria (CBN) and from selected mega banks' annual publication reports.The result of random effect regression provides evidence that capital adequacy, bank size, cost income ratio and income diversification have significant impact on financial performance of the banks under study.Based on the findings, the study recommends among others that a policy that will encourages banks to engage in non-interest income activities should be put in place since non- interest income has positive impact on financial performance.