As a biodegradable functional polymer, poly[(sodium acrylate)-co-(4-vinylpyridine)] [P(SA-co-4VP)] containing a small amounts of 4-vinylpyridine groups were prepared and their biodegradability, dispersity, and complex performance were analyzed. The polymers can be useful as detergent builders and dispersants. It was found that the biodegradation of P(SA-co-4VP) was more conspicuous when content of the 4-vinylpyridine in the copolymer was larger. This indicates that the 4-vinylpyridine, which acts as biodegradable segments, should be incorporated into the polymer main chain in such a manner that they are digested by activated sludge.