Abstract: The copolymerization of caprolactam(CPL) onto cellulose using potassium persulfate and ammonium persulfate as reaction initiator was studied. The molecular structure, morphology and crystallinity of graft copolymer were characterized using infrared spectrometer (FT-IR)，scanning electron microscope (SEM) and Xray diffractometer (XRD). Effects of various reaction parameters on grafting ratio, such as mass of monomer，concentration of initiator, reaction time and reaction temperature were evaluated. Results show that the optimum conditions are as follows: the mass ratio of monomer to cellulose 1∶1, initiator concentration 0.2 mol/L, reaction temperature 30 °C, reaction time 75 min. The grafting ratio reached 57% under the optimum conditions. The grafting occurs mainly on the surface and within the amorphous region of the cellulose, and the crystallinity is not destroyed.