The work of company needed by investors because could affect the willingness of investors to plant or withdraw their investments, instrument companies used in his work is earnings information. Earnings management is most used by companies is income smoothing. Agency theory the concept of income smoothing, pincipal and agents have motivation. This research to understand and explain; variable influence size firm, return on asset and the net profit margin partial against the income smoothing; variable influence size firm, return on asset and net profit margin simultaneously against the income smoothing. The kind of research used this research is an explanation with a quantitative approach. The variable in this research is size firm, return on asset and net profit margin as independent variables and income smoothing as dependent variable. This research used secondary data time series from the period 2012 to 2014. Data analysis method used is descriptive analysis and multiple linear regression analysis. The results of multiple linear regression analysis showed; there are partial effect between size firm variables, return on asset and net profit margin to the income smoothing; there is a partial effect between size firm variables, return on asset and net profit margin to the income smoothing.