We studied the interaction of water in poly(ethylene-co-vinyl acetate) of various vinyl acetate compositions and poly(vinyl acetate), on the basis of the infrared spectrum of the water dissolved therein. The spectrum shows a very sharp and distinct band at about 3690 cm(-1) (named as A), and less-sharp two bands around 3640 (B) and 3550 cm(-1) (C), the A band being outstanding especially at a low vinyl acetate composition. As the vinyl acetate composition increases, the A band decreases in intensity relative to the C band, whereas the B band increases contrarily. Analysis of the spectral change has elucidated that one-bonded water (of which one OH is hydrogen-bonded to the C=O of an ester group and the other OH is free) and two-bonded water (each OH of which is hydrogen-bonded to one C=O) coexist in the copolymer and that two-bonded water increases in relative population with increasing vinyl acetate composition. Dissolved water is entirely two-bonded in poly(vinyl acetate), in which C=O groups are densely distributed in the matrix. We proved that dissolved water in polymers is hydrogen-bonded through one or two OH groups to the possessed functional groups but does not cluster. (c) 2005 Wiley Periodicals, Inc.