The melt grafting of unsaturated silanes onto powdered polypropylene (PP) in a Haake TW100 twin-screw extruder and curing in hot water were studied. The influence of grafting formulations and extrusion conditions on the melt flow rates of grafted PP and the gel percentages of crosslinked PP was investigated. The gel percentages of methacryloylpropyltrimethoxysilane (VMMS)-grafted PP were markedly higher than those of vinyltriethoxysilane (VTES)- and vinyltrimethoxysilane (VTMS)-grafted PP, while significantly less degradation of PP during grafting was observed for VMMS-grafted PP. When benzoyl peroxide (BPO) was used as an initiator, no degradation of PP during grafting was observed, and the melt flow rates of grafted PP decreased with increasing BPO concentration. In contrast, use of dicumyl peroxide (DCP) as an initiator resulted in severe degradation of PP, and the melt flow rates of grafted PP increased gradually with increasing DCP concentration. BPO resulted in higher gel percentages than those of DCP at a fixed initiator concentration. Introduction of styrene into the grafting system greatly improved the gel percentage of crosslinked PP and reduced the degradation of PP during grafting. The optimum molar ratio of styrene to monomer is at about 1,5:1. Relatively low processing temperatures and high screw speeds are favorable.