In this work, we investigated the possibility to modify polyolefin surfaces by ring-opening metathesis polymerization (ROMP). We copolymerized propylene with a small amount of 1,7-octadiene in order to get a polyolefin with vinyl groups in the side-chains. By reaction of the ruthenium-carbene complex RuCl2(PCy3)(2)(=CHPh) 1 with the vinyl side groups, new carbene complexes were generated, thus creating the active sites for ROMP on the polyolefin surface. This procedure made it possible to graft polymers with different functionalities under mild conditions onto the hydrophobic polypropylene surface. The thickness of the modification depended mainly on the concentration of the active sites at the surface, on the time of treatment with monomer solution and finally on the solvent used for this treatment.