Free-radical grafting of glycidyl methacrylate (GMA) onto polypropylene (PP) powder was studied in a batch mixer. The reaction temperature was below the melting point of PP so that PP was modified in the solid phase. The graft yield of GMA obtained under various experimental conditions allowed for a good appreciation of the effects of chemical parameters (the concentration of monomer, initiator, and interfacial agent) and those of processing parameters (reaction time and temperature). Toluene was used as an interfacial agent to etch the surface of PP powder to provide more sites for reaction. Quantitative determination of the graft level was performed by wet chemical methods. The results showed that the solid-phase grafting could take place over a temperature range of 100-140 degrees C in the initiation of benzoyl peroxide (BPO). The ultimate GMA grafting level achieved was higher than that obtained in the melt state with dicumyl peroxide (DCPO) as a radical initiator. The grafting of GMA affected the crystalline morphology of PP and speeded up the crystallization process. The energy of activation and initial decomposition temperature of grafted samples were higher than those of ungrafted PP.