Alkali-assisted acid pretreated rice straw was saccharified using cellulase from Aspergillus niger BK01. The cellulase production by the fungus was enhanced by parametric optimization using solid-state fermentation conditions. Maximum cellulase production (12.0 U/gds of carboxymethyl cellulase, CMCase) was achieved in 96 h, using 6.0% substrate concentration, 7.5% inoculum concentration, 1:2 solid to liquid ratio, at pH 5.5, and temperature 28 °C, by supplementation of the fermentation medium with 0.1% carboxymethylcellulose and 0.1% ammonium nitrate. Characterization of crude cellulases showed that highest CMCase activity was observed at pH 4.8 and temperature 40 °C. The CMCase was stable from pH 4.8-5.5 and at a temperature range of 35-50 °C. The pretreated biomass was subjected to hydrolysis with the fungal cellulases. The saccharification optimization studies showed that 2% (v/v) enzyme concentration and hydrolysis time of 2.5 h were optimum for maximum yield, i.e, 23.78% sugars and 35.96% saccharification value.