An Endo-cellulase was purified to homogeneity using ammonium sulfate precipitation, ion exchange and size exclusion chromatography from newly isolated strain of Thermoascus aurantiacus RBB-1. The recovery and purification fold were 13.3% and 6.6, respectively, after size exclusion chromatography. The purified cellulase has a molecular mass (M) of 35 kDa. Optimum temperature for the enzyme was found to be 70 °C and stability was upto 80 °C for 1 h. Along with higher stability at 80 °C, enzyme showed half lives of 192 h and 144 h at 50 and 70 °C respectively. The purified cellulase was optimally active at pH 4.0 and was stable over a broad pH range of 3.0–7.0. The enzyme purified showed apparent Km and Vmax values of 37 mg/ml and 82.6 U/min/mg protein respectively with higher salt tolerance of 10% for 1 h.