Two types of microporous filter materials were developed for removing virus from water by using poly(N-benzyl-4-vinylpyridinium chloride) that captures virus in water. Conventional ultrafiltration using one to three sheets of 145-mu m-thick cellulose nitrate membrane with a pore size of 0.45 mu m and coated with 1.7 mg/g of poly(N-benzyl-4-vinyIpyridinium chloride-co-styrene) showed 99.4-99.998% removal (2.2-4.7 log(10)-unit reduction in concentration) of bacteriophage T4, whereas the control experiments using noncoated membrane showed 91-96% removal (1.0-1.4 log,,-unit reduction in concentration) of the virus. A composite 360-mu m-thick microporous membrane with a pore size of 20 mu m was prepared that consisted of connected minute beads of 1.7 mu m in diameter made of crosslinked poly(N-benzyl-4-vinylpyridinium chloride) and reinforced by a nonwoven cloth. Simple filtration using one sheet of the composite membrane at 34.2 cm/h showed 99.96-99.9995% removal (3.4-5.3 log(10)-unit reduction in concentration). The virus was not detected in the filtrate when two sheets of the composite membrane were used.