Thermosensitive 4VP-NIPAAm-4G copolymer beads containing pyridyl groups were first prepared by suspension copolymerization of 4-vinylpyridine (4VP), N-isopropylacrylamide(NIPAAm), and tetraethylene glycol dimethacrylate (4G; crosslinking reagent) in a saturated Na2SO4 aqueous solution in the presence of surfactant and MgCO3 as dispersants. Then the copolymer beads containing pyridinium groups were obtained by the quaternization of the copolymer beads with various alkyl iodides (CH3I, C4H9I, C8H17I) in N,N-dimethylformamide. The 4VP-NIPAAm-4G (15 : 97 : 3) copolymer bead and the 4VP-NIPAAm-4G copolymer beads quaternized with butyl iodide exhibited high thermosensitivity in water, although the 4VP-NIPAAm-4G copolymer beads quaternized with methyl iodide or octyl iodide hardly exhibited thermosensitivity. All the quaternized copolymer beads exhibited antibacterial activity against Escherichia colt (E. coli), although the 4VP-NIPAAm-4G copolymer bead did not. In particular, the copolymer bead quaternized with butyl iodide exhibited the highest antibacterial activity against E. coli at 30 degrees C. It was also found that the antibacterial activity of the quaternized 4VP-NIPAAm-4G copolymer beads was greatly affected by not only chain length of alkyl groups in alkyl iodides, with which the 4VP-NIPAAm-4G copolymer beads were quaternized, but also by temperature of the solutions. (c) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 2580-2589, 2010