Polypropylene (PP) was modified with maleic anhydride (MAH) via heterogeneous solid-state radical grafting performed in a fluidized polymerization reactor. The effect of PP morphology and different concentration of initiator (dibenzoyl peroxide, DBP) on the course of the reaction and grafting efficiency was evaluated with using infrared spectroscopy, scanning electron microscopy (SEM) and particle surface analysis (BET method). With respect to obtained results, the reaction course can be strongly affected by the reaction conditions and PP morphology. Unlike the reactive modification in melt, heterogeneous reaction exhibits lower extent of beta-scission albeit the reaction conversion is lower. Solid-state grafting can be used as an alternative method for the surface modification of nonpolar surfaces with polar monomers under mild conditions.