The title compound was synthesized by reducing (S)-1-benzyl-3-hydroxypyrrolidine-2, 5-dione with sodium borohydride-iodin. The raw material, intermediate, and the end product were characterized by IR spectra and the mechanism of reduction of imide by sodium borohydride-iodin was also studied by IR spectra. According to the IR spectra, it was concluded that the product was (S)-1-bezyl-3-hydroxypyrrolidine. The mechanism of the reduction is that borane, formed in situ by reacting sodium borohydride with iodine, partly was conjugated to carbonyl to form four-member-ring intermediate and partly conjugated to nitrogen. (S)-1-benzyl-3-hydroxypyrrolidine/BH3 complex was gained when the reduction finished. The title compound was obtained by removing borane from the complex in methanol.