Indonesian banking industry as a financial intermediary is demanded to be operate efficiently. Net Interest Margin value represent how effective the operational process. The focus study is to analyze how bank specification effect with credit risk, risk aversion, firm size and operational cost on net interest margin of Indonesia. In this research use probability sampling method to chose sample. Sample used in this research are public banking listed at Indonesia Stock Exchane on periode 2016 to 2018. Data analysis was done using Microsoft Excel 2010 and using E-Views 10 program for descriptive statistic analysis, hypothesis testing in this research using data panel regression with Fixed Effect Model.This research of study finds that net interest margin have negative influenced by firm size. Credit risk, risk aversion and operational cost have no influenced on net interest margin.