Nowadays, the development of Sharia Banks (SB) in Indonesia has shown positive results. However, the development of SB is still slow because their competitiveness levels are lower than those of conventional banks, which is proven by the small market share. One attempt to gain competitiveness is by maintaining efficiency that could constantly and significantly boost the development. This paper aims to estimate factors that affect the efficiency of Sharia banks in Indonesia. The use of panel data of 11 public SB from 2012 – 2016 and random effect regression illustrate how CAR, ROA, ROE, NPF, FDR and Number of Branches (NB) affect efficiency. In particular, we use Operating Expense Ratio (OER) to determine the efficiency level of Sharia Banks. The estimation finds that ROA, FDR, NB have a negative correlation toward OER, NPF has positive effect, and CAR as well as ROE do not significantly affect OER.