Human capital efficiency Structural capital efficiency Capital employed efficiency Board size, board of demography Return on assets Assets growth. This study aims to examine and analyze the determinant of financial performance (return on assets), namely intellectual capital that consist of human capital, structural capital, capital employed and good corporate governance (GCG) that consist of board size and board of demography and its impact on the growth of Islamic banks assets in Indonesia for the period 2014-2018. Research data is annual report and GCG report of 12 Islamic banks in Indonesia for the period 2014-2018. The sampling method used was purposive sampling from 12 Islamic banks met the criteria to be the sample. The method of analysis used in this study is multiple linear regression. The results showed by model-1 that intellectual capital measured by human capital efficiency (HCE), structural capital efficiency (SCE) and capital employed efficiency (CEE) and GCG measured by board size (BS) and board of demography (BD) simultaneously are having significant influence to the return on assets (ROA) of the banks. The results showed by model-2 that intellectual capital measured by human capital efficiency (HSE), structural capital efficiency (SCE) and capital employed efficiency (CEE) and GCG measured by board size (BS) and board of demography (BD) simultaneously are having nonsignificant influence to the assets growth (AG) of the banks. Contribution/Originality: This study contributes to the existing literature by examining and analyze the determinant of financial performance (return on assets), namely intellectual capital that consist of human capital, structural capital, capital employed and good corporate governance (GCG) that consist of board size and board of demography and its impact on the growth of Islamic banks assets in Indonesia for the period 2014-2018. 1. INTRODUCTION The development of Islamic banks in Indonesia is significant; it is due to the legalization law of Islamic banking in 2008 which became a factor driving the growth of Islamic banks in Indonesia. In order to meet ASEAN Economic Community Banking in 2020 the financial services industry competition will be more stringent, for which Islamic banks are required to continue to grow (Siswanti et al., 2017). As a concrete step in the efforts to develop Islamic banking in Indonesia, Bank Indonesia has formulated a Grand Strategy for Islamic Banking Market Development, as a comprehensive strategy for market development covering strategic aspects, namely: Establishing a vision of 2010 as the leading Islamic banking industry in ASEAN, image building new national Islamic banking that is inclusive and universal, more accurate market mapping, more diverse product development, service improvement, and new communication strategies that position Islamic banking more than just banks. The volume of Islamic banking business in the past three years, particularly Islamic Commercial Banks (ICB) and Islamic