1,6-Hexanediol diacrylate (HDDA), pentaerythrithyl tetramethacrylate (PETMA), and triallyl-isocyanurate (TAIC) were used as representative monomers to modify polypropylene (PP) in the presence of dicumyl peroxide (DCP) in a mixer. Fourier transformed infrared spectroscopy (FTIR) results confirmed that all the three polyfunctional monomers have been grafted on PP backbone. The shape of torque curves suggested the occurrence of grafting and/or crosslinking structure. The rheological behaviors of HDDA modified PP showed the highest G and lowest tan at low frequency, shear-thinning shifted to lower frequency in *- plot, as well as more deviation from semicircle characteristic of linear PP at high viscosity in Cole-Cole plot. And, the improvement of the mechanical properties followed the order as below: TAIC < PETMA < HDDA. Meanwhile, the foamability of the modified PP samples was also investigated. The cellular structure and morphology of the obtained foams were observed by scanning electron microscopy (SEM), and the results indicated that the foamability of the three modified PPs followed the same order, demonstrating HDDA modified PP foam possessed the highest cell density and expansion ratio, and the most well-defined closed cell structure and uniformly cellular morphology. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1675-1681, 2013