Pentaerythritol triacrylate (PETA) was successfully grafted onto the plasma-treated isotactic polypropylene (iPP) via the in situ melt processing. The X-ray photoelectron spectroscopy (XPS) results showed that the hydroxyl and carbonyl groups, and peroxides could be generated via plasma treatment. The content of free radical in plasma-treated iPP (PiPP) was measured by 2,2-diphenyl-1-picrylhydrazyl (DPPH). It was found that the resulting peroxides induced the grafting copolymerization of PETA onto iPP, and the grafted PETA promoted the formation of beta-crystal in PiPP, which was evidenced by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) measurements, respectively.