Grafting of maleic anhydride (MA) onto isotactic polypropylene (iPP) was carried out by thermal decomposition of dicumylperoxide (DCP) using supercritical carbon dioxide (scCO(2)) as a solvent and swelling fluid. Provided that the initial concentration of anhydride dissolved in scCO(2) is higher than 1% w/w, the grafting occurs without significant molecular weight modification of the polymer, and with a proper selection of the operative conditions, a grafting level higher than 0.5% w/w with respect to the polymer mass was obtained. The amount of grafted MA was determined by FT-IR spectroscopy and polymer degradation was monitored by dynamic mechanical tests in the melt state. The effect of MA and DCP concentration, of the scCO(2) density, and of the reaction time on the grafting yield and on the melt flow behavior was studied. Maleic anhydride homopolymerization during the grafting is suggested by FTIR spectra. The home-synthesized maleated iPP was used as effective compatibilizing agent in the preparation of iPP/Nylon-6 blends.