In this paper, the authors reported on the antimicrobial activity of purified and hydrolysed chitosan against two yeast strains: Saccharomyces cerevisiae and Pichia pastoris X33 and one fungal strain Aspergillus niger 015. The minimum inhibitory concentrations (MICs) of purified chitosan were 2.5 and 0.625 mg/ml
of hydrolysed chitosan were 0.625 and 0.313 mg/ml for the yeast Saccharomyces and Pichia, respectively. The MICs of chitosan derivatives for the fungus Aspergilus were both 3.75 mg/ml. Hydrolysed chitosan showed higher inhibition efficiency than purified chitosan in a/l cases. For fungus, the higher chitosan concentration of both types the greater inhibition activity on fungal spore formation was proved.