Aims: The cellulase complexes of Trichoderma reesei are relatively low in endoglucanase and β-glucosidase activity compared with exoglucanase. The aim of this study is to determine the effect of Humicola insolens recombinant endoglucanase on the activities of commercial cellulases, Celluclast® and Acellerase® BG, during the hydrolysis of pretreated oil palm empty fruit bunch (OPEFB) fibres to simple sugars. Methodology and results: An endoglucanase (CMC3) from H. insolens ATTC 16454 was expressed in Pichia pastoris. The recombinant protein was purified and verified by SDS-PAGE and Western blot. The enzymatic hydrolysis of OPEFB fibres was carried out at 55 °C for 72 h and 1:40 and 1:100 mixtures of CMC3 and Celluclast® were used. All reaction mixtures were added with commercial β-glucosidase, Accelerase® BG, at a fixed concentration of 116 mg/mL. The sugars produced were analysed by high-performance liquid chromatography. Two sugar peaks were successfully resolved at different retention times and were identified as xylose and glucose. At Celluclast®-to-CMC3 activity ratio of 1:100, the highest reducing sugar concentration was obtained, whereby the glucose and xylose production increased by ~59% and ~27%, respectively. Conclusion, significance and impact of study Recombinant CMC3 can act synergistically with Celluclast® and Accelerase® BG to increase the production of glucose and xylose from pretreated OPEFB fibre. This study contributes greatly towards the development of efficient cellulase enzyme cocktail for the efficient hydrolysis of OPEFB biomass and the production of simple and fermentable sugars.