Synthesis and radical polymerization behavior of N-vinylsaccharin (1) are described. Radical homopolymerization of 1 was carried out in the presence of a radical initiator for 24 h to afford the polymer containing a saccharin moiety in the side group, which was insoluble in common organic solvents. Among the copolymers of 1 with various vinyl monomers such as vinyl acetate (VAc), methyl acrylate (MA), acrylonitrile (AN), and styrene (St), only the copolymer [copoly(1-St)] obtained from 1 and St was soluble in common organic solvents. In the copolymerization of 1 and St, the Q and e values of 1 were estimated to be 0.10 and -1.60, respectively. These values are similar to those of N-vinylphthalimide (Q = 0.36, e = -1.52). The reaction of copoly(1-St) with LiAlH4 was carried out in THF for 24 h to convert the saccharin moiety into the ring-opened structure bearing hydroxy and sulfonamide groups.