Abstract: The wastes materials from the sweet orange (Citrus sinensis) were used as substrate for the production of cellulase. The rind, the pericarp or albedo and the pulp were hydrolyzed by cellulolytic enzymes of Trichoderma longibrachiatum, Aspergillus niger and Saccharomyces cerevisiae after they were treated with alkali and steam. The amount of glucose released from the substrates following the secretion of cellulase by the three microorganisms was measured. The orange wastes released amounts of glucose ranging from 0.76-0.96 mg mL-1 by Trichoderma longibrachiatum, 0.90-1.08 mg mL-1 by A. niger and 0.60-0.76 mg mL-1 by S. cerevisiae after five days of fermentation. The conditions of the fermentation were then varied to determine their effect on cellulase production. Fermentation parameters varied were time, pH, substrate concentration, temperature and inoculum size. After this, conditions that produced highest amounts of glucose were combined in an optimization experiment. Glucose production under optimized conditions were 0.94 mg mL-1 by T. longibrachiatum, 0.83 mg mL-1 by A. niger and 0.67 mg mL-1 by S. cerevisae. The activity of the test organisms` cellulase against CMC on the orange wastes was also determined with T. longibrachiatum producing 3.86 mg mL-1, A. niger 2.94 mg mL-1 and S. cerevisiae 2.30 mg mL-1 glucose amounts all from orange pulp.