The synthesis of polynorbornene by ring opening metathesis polymerization (ROMP), in the presence of 1st and 2nd generation Grubbs catalyst-functionalized multiwalled carbon nanotubes (MWCNT), has been studied. MWCNTs were obtained by catalytic chemical vapour deposition (CCVD) of ethylene. A full characterization of the 1st and 2nd generation Grubbs catalyst-functionalized nanotubes was performed by FTIR and TG-DTG-MS. The amount of catalyst grafted to the nanotube surface was estimated. The activity of the catalyst-functionalized nanotubes in ROMP of 2-norbornene was found to be similar to that of bare 1st and 2nd generation Grubbs catalysts. The characterization of polynorbornene-carbon nanotube composites shows that the nanotubes are well dispersed in the polymer matrix.