The industrial process for extracting chitosan from low cost shellfish waste is well known. It comprises three basic steps: deproteinization, demineralization of the shells to yield chitin, followed by deacetylation of chitin to produce chitosan. However, the product obtained from the process often still contains many impurities. In general, these encompass minerals and carotenoids bonded to chitosan. The treatment of chitosan flakes with aqueous solutions of inorganic polybasic acids permits the removal of the impurities mentioned above. This paper describes an engineering-type procedure which develops a pure, colorless material having a controlled molecular weight.