Commercial banks can be said to be effective in intermediary function as an institutions intermediaries when followed by a high level of efficiency in their business activities . This study aims to determine: 1 . Is of banks ( measured by LDR or FDR ) influence on the efficiency of Conventional Banks and Islamic Banks ( measured by OEOI ) , 2 . Is there a difference level of effective intermediation function between Conventional Banks and Islamic Banks ? The analysis technique used by multiple regression is to obtain an overall picture of the relationship and influence between the dependent and independent variables , and used different tests to see the difference in the level of efficiency . The object of this research is a conventional banks and Islamic banks operating in Indonesia starting in April of 2010 ( the start time separated financial statements of a conventional bank and Islamic banks ) until September 2013 by using the times series of data monthly . The samples were used together with the population . The analytical method used is multiple regression analysis using secondary data and to determine the accuracy of the model testing of some of the underlying assumptions of classical regression models include test , multicollinearity , and autocorelations heteroscedatis , and use average different test analysis. LDR and FDR has a negative effect on ROA and showed statistically significant, it means that when the effective intermediation functiong of conventional banks and Islamic banks increases, there will be increase in efficiency (because the value OEOI down). Based on the average difference test showed that there were significant differences between the effectiveness of intermediation between Conventional Banks with Islamic Banks.