Graphene nanoribbon (GNR) is a quasi one-dimensional film, in which a bandgap exists through the quantum confinement and/or localization effect. Compared to bulk graphene, GNR has high potential in achieving high I on/Ioff ratio. The carrier mobility of GNR, however, exhibits strong degradation because of the uncontrollable edge roughness and/or states. Most reported GNR-FETs are patterned using ebeam-lithography processes, where the spot size of the electron beam limits the edge smoothness1. In this work, we present a GNR fabrication method based on a nanowire-mask, where the edge roughness is determined by the surface roughness of the nanowire (<1nm) 2. With four-terminal measurement setup, single layer nanoribbon (SLR) devices show μhole∼1180cm2/(Vs), Ion/Ioff >7 and low frequency noise figure A∼10-6 at 300K. Moreover, short-channel SLR (∼250nm) shows conductance quantization at 77K3, and confirms that the quasi-ballistic transport properties can be achieved through this method.