The present invention relates to a wind turbine rotor blade comprising a lightning protection system. The lightning protection system comprises a lightning receptor for capturing lightning strikes. The receptors are arranged in the rotor blade. The lightning receptors comprise carbon nanotubes. In embodiments, the nanotubes are at an exterior surface is provided with a layer of carbon nanotubes and/or at least part of the lightning receptor is of a carbon nanotube metal composite material, such as a carbon nanotube metal matrix composite material. Moreover, the exterior surface of the receptor may in embodiments be provided with one or more electric field enhancing protrusions.