Dispersion polymerization of styrene was performed in the presence of poly(N-vinylpyrrolidone)(PVP) with the photoiniferter groups as the stabilizer under UV radiation. Poly(N-vinylpyrrolidone-co-4-vinylbenzyl chloride) [P(VP-co-VBC)] was first synthesized by a free radical polymerization. The VBC units were then, modified to dithiobenzoate and diethyldithiocarbamate as the photoiniferter groups. The contents of the photoiniferter groups were 1.7, 2,4 and 4.2 mol%. Polystyrene(PSt) particles prepared using PVP stabilizers with dithiobenzoate groups(PVPDTB) had a spherical shape. On the other hand, PSt particles obtained using PVP stabilizers with diethyldithiocarbamate groups(PVP-DTC) showed a crumpled appearance. The mean diameters of the PSt particles decreased with increase in the contents of photoiniferter groups in the PVP stabilizers. Nano-sized PSt particles(80-90 nm) could be synthesized by using PVP-DTB. PSt particles prepared using PVP-DTC had a crosslinked structure.