This research aims to analyze and verify the bank size, profitability, liquidity, credit risk, and income diversification as the determinant of bank’s operating efficiency in Indonesia. In this research, the bank’s operating efficiency proxied with the Operating Expense to Operating Income (OEOI) and Net Operating Margin (NOM). The sample selection using purposive sampling method and the samples are 81 Conventional Banks in Indonesia in 2011–2016. The data is analyzed using Structural Equation Modelling (SEM) with SmartPLS Software. The results show that bank size, profitability, and income diversification have positive influence towards bank’s operating efficiency. Whereas, bank liquidity and credit risk have negative influence towards bank’s operating efficiency.Keywords: Bank’s operating efficiency, bank size, profitability, liquidity, credit risk, and income diversification. ABSTRAKTujuan penelitian ini untuk menganalisis dan membuktikan ukuran, profitabilitas, likuiditas, risiko kredit, dan diversifikasi pendapatan perbankan sebagai determinan efisiensi operasional perbankan di Indonesia. Dalam penelitian ini, efisiensi operasional perbankan diproksikan dengan Biaya Operasional terhadap Pendapatan Operasional (BOPO) dan Net Operating Margin (NOM). Pemilihan sampel menggunakan metode purposive sampling sehingga diperoleh sampel sebanyak 81 Perbankan Umum Konvensional di Indonesia tahun 2011–2016. Data dianalisis menggunakan Structural Equation Modelling (SEM) dengan software SmartPLS. Hasil penelitian menunjukkan bahwa ukuran, profitabilitas, dan diversifikasi pendapatan perbankan berpengaruh positif terhadap efisiensi operasional perbankan. Sedangkan likuiditas dan risiko kredit perbankan terbukti berpengaruh negatif terhadap efisiensi operasional perbankan.Kata Kunci: Efisiensi operasional perbankan, ukuran perbankan, profitabilitas perbankan, likuiditas perbankan, risiko kredit perbankan, dan diversifikasi pendapatan perbankan.