High melt strength polypropylene (HMSPP) was prepared by in situ heat induction reaction, in which pure polypropylene (PP) powders without any additives was used as basic resin, and low density polyethylene (LDPE) and trimethylolpropane triacrylate (TMPTA) were added as blending resin and as cross-linking agent, respectively. Microstructure of the obtained HMSPP (PP/LDPE/TMPTA blends) was characterized by FTIR, Wide-angle X-ray diffraction (WARD), and testing of gel content. The effect of LDPE content on melt strength and melt flow rate of HMSPP were investigated. When the content of LDPE was 40 wt %, the melt strength of the HMSPP was above 16 CN, which was much higher than those of pure PP powder (2.6 CN) and PP/LDPE blends without TMPTA (6.1 CN). Moreover, thermal behavior and mechanical properties of the HMSPP were also investigated. The results showed that the thermal stability and impact strength of HMSPP were greatly improved. In addition, HMSPP possessed good processing performance and good foaming properties. The foams produced by HMSPP showed uniform, closed, and independent cells. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 1739-1746, 2010