Ionic liquids (ILs) are regarded as green solvents and have demonstrated ability in the solvation of lignocellulosic material, thus promoting its enzymatic hydrolysis by cellulases. In this study, cellulase (PKC-Cel) obtained from Trichoderma reesei (RUTC30) through fermentation displayed good stability in choline acetate ChoOAc, a biodegradable IL. Empty fruit bunches (EFB) were subjected to single-step hydrolysis in an IL-enzyme system. Response surface methodology was employed to maximize ethanol production. Three parameters were optimized, namely sugar loading, inoculum concentration, and agitation. The distilled ethanol purity was 98.6% (v/v). The ethanol yield was 87.94% of the theoretical yield, which was 0.275 g ethanol g�1 EFB. In comparison, the non-IL system produced 0.127 g g�1 EFB. The yield coefficients (Formula presented.), (Formula presented.), and (Formula presented.) were 0.552, 0.148, and 3.69 g g�1. The specific growth rate (Formula presented.) was determined to be 0.264 h�1 and the (Formula presented.) was 0.777 h�1. © 2019 Informa UK Limited, trading as Taylor & Francis Group.