Zinc oxide (ZnO) nanorods have been synthesized via the arc discharge method. Different cathode materials, graphite and copper, were applied to modulate the morphology and UV & humidity sensing properties of the as-synthesized ZnO nanorods. Compared with ZnO nanorods synthesized by graphite cathode, shorter length and other spherical and cubical structures were also detected for those ZnO nanorods synthesized by copper cathode. A better UV-sensitive photoconduction and higher humidity sensitivity were detected for ZnO nanorods synthesized by graphite cathode than those obtained by copper cathode, which is considered to be due to the higher aspect ratio for long ZnO nanorods. The simplicity of the synthesis route coupled with the modulation of morphology and sensing properties of ZnO nanorods make the arc discharge method a very promising way to produce high quality ZnO nanorods with adjustable morphologies.