Block copolymers composed of 2-(alpha-D-mannopyranosyloxy)ethyl methacrylate (ManEMA) and 2-(N, N-dimethylamino) ethyl methacrylate (DMAEMA) were synthesized by aqueous RAFT polymerization. The number-average degree of polymerization (DPn) of ManEMA segments was constant at 33, and the DPn of DMAEMA segments varied from 98 to 241. Statistical copolymers with a similar composition were also prepared via aqueous RAFT polymerization. The mannose-presenting nature was evaluated by a turbidimetric assay using Concanavalin A. The clustering rate of statistical copolymers was faster than those of the corresponding block copolymers. By contrast, no significant differences between block and statistical copolymers were found in their DNA-condensing ability as evaluated using gel shift assays and in their cytotoxicity in the transfection of plasmid DNA (pEGFP-N1) to HeLa cells. However, the overall transfection efficiency significantly depended on the monomer distribution. Statistical copolymers showed an overall transfection efficiency comparable to those of poly(DMAEMA center dot HCl)s, but block copolymers showed no detectable transfection under the same conditions.