Chemical pesticides are highly hazardous to humans and animalsand not very biodegradable, they frequentlypollute water and soil. A sustainable healthy environment needs ‘‘green’’ pesticides. This review describes the chitosan, structurally, chitosan is a straight-chain copolymer composed of D-glucosamine and N-acetyl-D-glucosamine being obtained by the partial deacetylation of chitin, as well as different sources and the conditions of chitosan preparation are also discussed.The chitosan can be isolated from crustacean such as crabs and shrimps as well as insects and fungi.Finally, several selected chemical and biomedical applications are presented, in which chitin and chitosan being recognized as novel biomaterials due to advantage of their biocompatibility and biodegradability.