It was firstly demonstrated that the resistance of bridging GaN nanowires (NWs) can be in situ controlled via current driven self-heating. Owning to the absence of contact barrier at the electrodes of bridging NWs, the Joule-heating can be generated mainly on the NW itself rather than on the electrodes. With increase of NW bias -voltage (BiV) from 2.5 V to 10 V, the generated Joule-heating can make the NW oxidized in air, which leads to about 700 fold increase in NW resistance (from 82.5 omega to 6 x 10(4) omega). Theoretical simulation indicated that a NW temperature of 649 K can realized with a BiV of 4 V, which agrees well with the observation of thermal emission microscope. Moreover, the measured oxygen composition in the NWs was increased with increasing BiV, which indicates that the NWs were oxidized by BiV induced self-heating. This work provides a simple method for precise control of NW resistance, which can be further applied to the formation of core/shell NWs with real time monitoring.