A process for producing a salt of a chitosan acid anion derivative, which comprises contacting chitosan fibre (a) with a base in an aqueous or non-aqueous medium and (b) with a solution in an aqueous or non-aqueous medium of a salt of the formula (I): M-R-T wherein M is a Group IA metal cation R is a hydrocarbyl oxoacid anion, substituted by T and T is a nucleophilic leaving group, all at a temperature below 50° C., preferably in the range of 30 to 40° C.
