Chitosan, chitooligosaccharides and their derivatives have potentially high commercial value. These products are bio-cidal to a broad spectrum of pathogenic microorganisms, insects and pests. Chitindeacetylases play very important role in biological attack and defence system, biological control of fungal plant pathogens. Chitosan derivatives have potential for removal of various aquatic pollutants and detoxification of water and waste water. Naturally occurring amino-polysaccharides have unique physicochemical characteristics and biological activities in agri cultural operations like seed priming coating and spray agents having barrier properties. The patent effect of chitosan derivatives on plant disease control, growth promoter, elicitation of defence responces, thus preserving crop yield and quality.