Straight and zig-zag isolated GaN nanowires were investigated for their electrical properties using focused ion/electron beam (FIB/FEB) deposited platinum contacts. The straight and smooth nanowire with FIB contacts was non-ohmic and relatively high leakage current was observed under reverse bias. The straight and smooth nanowire with FEB contact shows ohmic behaviour whereas the zig-zag nanowire shows non-ohmic with negative differential resistance (NDR). The peak-to-valley current ratio was about 4.5 at room temperature under forward bias. The NDR observed in the zig-zag nanowires has been explained based on inelastic tunnelling through electrically active acceptor-like defect states present within the bandgap.