An attempt has been made to give biodegradability to poly(vinyl acetate) by partial modification of the chemical structure. Poly(vinyl acetate) containing a small amount of N-benzyl-4-vinylpyridinium chloride (PVAc-co-VPC) and that containing 16 mol % of methyl acrylate and a small amount of the pyridinium group (PVAc-co-MA-co-VPC) showed significant degradation when placed in an aeration tank of sewage works. Control polymers possessed of no pyridinium group did not show significant degradation under these conditions, and the extent of weight reduction during the treatment increased with the content of the pyridinium group. The weight reduction exhibited an uppermost limit after 7 days of the treatment, and the pyridinium group disappeared from the polymer during the early period. Incorporation of the pyridinium group into poly(vinyl acetate) appeared to have improved the biodegradability. Gel permeation chromatographic analysis showed that the low molecular weight fraction was more easily degraded than was the high molecular weight fraction. In the degradation of PVAc-co-MA-co-VPC, the unit of methyl acrylate was more easily removed than that of vinyl acetate.