Macroporous crosslinked acrylonitrile-divinylbenzene copolymer beads were synthesized by suspension polymerization technique. The beads were chemically modified to have amidoxime functional group, which was used as a solid support for anchoring copper microparticles. The copper ions loaded on the copolymer beads were reduced using strong reducing agent to have copper microparticles on the amidoxime copolymer beads. The size of copper particles formed depends upon the amount of copper ions loaded on the beads. The formation of copper microparticles on the copolymer was confirmed by instrumental analysis. The copper containing amidoxime copolymer beads were investigated for the biocidal activity. The size and the distribution of copper particles on the amidoxime copolymer beads influenced their biocidal activity. The biocidal activity was tested against two Gram-positive bacteria, Bacillus subtilis and Staphylococcus aureus, and against two Gram-negative bacteria, Pseudomonas aeruginosa and Escherichia coli. The beads containing copper particles showed better biocidal activity against the Gram-negative bacteria when compared with the Gram-positive organisms. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013