Abstract: Aspergillus niger isolated from diseased yam in three yam-growing zones in Nigeria synthesized cellulase (EC.3.2.1.4) which caused soft rot of the yam within nine days of inoculation. Microscopic and molecular analyses revealed two isolates of A. niger, P1 and P2, from yam growing in tropical rain forest and southern guinea savannah produced cellulase enzymes in significantly different proportions. When the protein extracts from the infection were subjected to molecular exclusion chromatography, three peaks of absorption (A, B and C) were produced with only the components of peak A showing cellulase activity.