The viscometric coefficient, kAB, characterizing the interaction of chemically dissimilar polymer segments was estimated from changes of the intrinsic viscosity of chitosan in “pseudosolvents,” i.e., dilute solutions of poly(ethylene glycol) (PEG) in a solution of 0.1 M acetic acid/0.2 M sodium acetate (1:1). The blends were studied at 25°, 35°, and 45°C. The miscibility between chitosan and PEG was found to increase with the temperature of the measured systems and to decrease with increasing molar mass of PEG. In the cases where favorable compatibility was exhibited between chitosan and PEG, H-bonding interaction between the two polymers should be strong enough to overcome the intra- and intermolecular H-bonding among chitosan chains.