Banking is a company that offers products in the form of services. Seeing this, the existence of customer trust is one of the important factors in smooth operations. Seeing this, Islamic banking as a type of banking requires good financial performance. Of course, this will make many investors come and make transactions at the bank. Therefore, the purpose of this research is to analyze the effect of non-performing financing (X1) and bank size (X2) on the so-called Return of Assets (ROA) (Y) in Islamic Commercial Banks. The method used to analyze this relationship is a quantitative method. The population taken is Islamic Commercial Banks in Indonesia. The year of focus is 2014-2020. The research subjects are in five Islamic banks, namely, PT. Bank Syariah Mandiri, PT. BCA Syariah, PT. Bank Muamalat Indonesia, PT. BRI Syariah, and PT. BNI Syariah. The data taken is secondary data and library research. The data was collected by using documentation study technique where the data were collected by category and classification of written materials that have a relationship and support the running of the research. The results obtained are the independent variable NPF (X1) has a large influence on ROA (Y), which is caused by the significance level of the variable is smaller than the 0.05 level of significance. On the other hand, the independent variable Bank Size (x2) does not have a major influence on ROA (Y) because the significance level of the variable exceeds 0.05. The results of the coefficient of determination between NPF (x1) and Bank Size (x2) on the profitability of Islamic banks (ROA) (Y) obtained the value of R2 (0.288) or 28.8% NPF variable (X1) and bank size (X2) affects ROA (Y). While 71.2% is influenced by other variables that are not included in this study.