The room-temperature functionalization reaction between poly(styryl)lithium and propylene oxide in benzene was studied. The functionalized polymer was characterized by H-1 NMR, C-13 NMR, and APT-C-13 NMR. C-13-methyl-labeled propylene oxide-functionalized polystyrene was also synthesized and characterized. Hydroxylated polystyrene was obtained in only 93% yield, but with high regioselectivity (97% of addition of the anionic chain-end to the least substituted carbon of the propylene oxide ring) and no oligomerization. The lower than quantitative yield was ascribed to the proton-transfer reaction of poly(styryl)lithium from the methyl group of propylene oxide, which formed unfunctionalized polystyrene.