Chitosanase, a new class of enzymes with antifungal properties was induced by toxigenicAspergillus flavusin both germinating corn and peanut seeds. The enzyme was partially purified and fractioned by SDS‐Polyacrylamide Gel Electrophoresis activity and copolymerized with chitosan or glycolchitosan as substrate, then quantified by scanning densitometry and a 2‐dimensional analysis software program. Chitosanase enzyme was markedly induced by toxigenicA. flavusgrowing in germinating corn and peanut seeds, as compared to control (water) which showed the lowest activity (almost nil in corn). However, chitosanase induction was higher in seeds treated with chitosan from Crustacea. Overall, enzyme activity was higher in peanut than in corn seeds. However, electrophoresed gels from peanut treated withA. flavusor water showed more polypeptides (three and one, respectively) than gels from corn seeds, which only showed one polypeptide for bothA. flavusand water treatment. The enzyme molecular weight was estimated to be between 36000 and 45000.