A novel strategy was developed by melt grafting reaction in the presence of macromonomer vinyl polydimethylsiloxane (VS) and comonomer styrene (St) for preparing high melt strength polypropylene (HMSPP), and the rheological behavior, melt strength, and foaming ability of HMSPP were investigated. The results showed that VS and St were successfully grafted onto isotactic polypropylene (iPP), and the melt strength of HMSPP increased by more than 12 times compared to that of the virgin iPP. Moreover, HMSPP exhibited excellent foaming ability with smaller cell size, higher cell density, and higher expansion ratio compared to the virgin iPP when supercritical carbon dioxide was used as the blowing agent. POLYM. ENG. SCI., 55:251-259, 2015. (c) 2014 Society of Plastics Engineers