Significant increase in extracellular cellulase and hemicellulase activities was observed in the biosynthesis of cellulase enzyme in mixed culture fermentation of Trichoderma reesei D 1–6 and Aspergillus wentii Pt 2804 when the A. wentii inoculation was phased by 15 h. The optimal conditions of fermentation by the mixed culture have been established. Presence of mannanase has been found to affect the release as well as activity of cellulase enzyme produced in mixed culture. Copyright © 1985 John Wiley & Sons, Inc.