An improved method is described for the production of chitosan from mycelia of the fungus Gongronella butleri, grown by solid substrate fermentation on sweet potato. The chitosan was extracted subsequently by 11 M NaOH at 45 degreesC, and 0.35 M acetic acid at 95 degreesC. The resulting extract was clarified using a heat-stable, commercial alpha-amylase. The yield (4-6 g/100 g mycelia) and relative number average molecular weight (44-54 kDa) of the chitosan increased with increasing duration of fungal growth up to the sixth day.