The existing methods of preparing polymer blends of cellulose, chitin and chitosan with natural and synthetic polymers and their applications are reviewed. The methods of solid-phase blending of these polymers under conditions of joint action of high pressure and shear deformation are discussed. Normally, under these conditions the processes of dispersion of polymer particles, amorphization, mixing at different levels, depolymerization as well as a chemical interaction resulting in formation of branched and crosslinked structures can take place. The probability and intensity of these processes depend in many respects on the type and magnitude of the external force, but the properties of the polymers are of higher importance. The advantages of the method of joint action of high pressure and shear deformation compared to the conventional techniques of polysaccharides mixtures production are shown.