Clear blends of chitosan acetate salt with poly (N-vinyl-2-pyrrolidone) (PVP) made from aqueous solutions look to be miscible on appearance. IR spectra investigated the carbonyl-hydroxyl hydrogen bonding between chain-chain in the blends and thus evidenced the compatibility of two polymers on a molecular level. The IR spectra, DSC also explored the interaction changing during the temperature increasing and indicated that a significant conformational change took place. Introduction Chitin is one of the most abundant natural polymers being second only to cellulose in the amount produced annually by biosynthesis'. It occurs in animals, particularly in crustaca, molluscs and insects, where it is an important constituent of the exoskeleton, and in certain fungi where it is the principal fibrillar polymer in the cell wall. Chitosan is a product obtained by alkaline deacetylation of chitin and has good properties for forming membrane. In dehydration of solvents, e.g. ethanol, pyridine, the pervaporation performances were fully investigated and the results showed it was an excellent membrane 2,3 . But it has little permeability for MeOH/MTBE mixture, probably due to its rigid chain and close packing with presence of several different types of intermolecular and intramolecular hydrogen bonding in polymer matrix, and thus up to now there is no any report on this. But with poly (N-vinyl-2-pyrrolidone) (PVP) blending with chitosan, the obtained polyblend membrane showed good pervaporation permeation for methanol(MeOH)/methyl tert-butyl ether(MTBE) mixture 4 . The possible explanation should contribute to the structure characteristics of polyblends, particularly the interaction between chain-chain of two amorphous polymers 5,6 . A number of papers reported the miscibility behavior in blends composed of polymers with dissimilar chemical structures, which provide specific interactions between chains. Miscibility of blends containing donor and acceptor polymer like those containing acid and/or basic units has been reported. It has demonstrated that poly (N-vinyl-2-pyrrolidone) interacts strongly with polymers of a wide variety of polymers, e.g. poly(vinylidene fluoride) 7 , polyvinlyalcohol 8 , poly(2,6-dimethlyt-1,4-phenylene oxide) 9 , poly (mono-n-alkylitaconates) 10 poly (N-l-alkyitaconamic acids), cellulose 12 etc. However, to our knowledge, no works dealing with blends containing chitosan acetate salt and poly (N-vinyl-2-pyrrolidone) have been reported. Our earlier interest was the membrane pervaporation properties, but the membrane showed good permeability for MeOH/MTBE mixture, particularly compared with chitosan membrane. For this reason, the structure characteristics of polyblends of chitosan acetate salt and poly (N-vinyl-2-pyrrolidone), particularly the hydrogen-bonding interaction between chain-chain in polyblends, were investigated by IR, DSC.