Abstract: The present study deals with isolation, screening and optimization of cultural conditions for biosynthesis of cellulases by Trichoderma harzianum using agricultural byproduct. Twenty different strains of Trichoderma harzianum were isolated from different soil samples by serial dilution method. Of all the strains tested, KM07 gave maximum production of cellulases by solid-state fermentation. Different agricultural byproducts such as wheat bran, wheat straw, rice bran, rice husk and soybean meal were tested for the production of cellulases and wheat bran was found to be the best substrate. The production of enzyme was significantly improved as the wheat bran was moistened with mineral salts CMC solution (ratio 1:1). The cultural conditions such as temperature 28°C and pH 6.5 were also optimized. The production of cellulases was maximum 72 h after the inoculation.