Highly dispersed gold (Au) nanoparticles (NPs) supported on nitrogen doped multi-walled carbon nanotubes (NCNTs) were synthesised using a simple electrochemical method. Morphology of Au-NPs and their dispersion profile were studied depending on the applied potential and deposition duration. Novel conductometric gas sensors were developed from the thin films of Au-NPs/NCNTs nanocomposites and evaluated towards H2 gas. Electron microscopy revealed that the Au-NPs were deposited homogeneously on the outer surface of the NCNTs. The average size of the Au-NPs is 5 nm when the applied potential is 10 V for 10 mins and 10 nm when the applied potential is 20 V for 10 mins. The sensors were exposed to different concentrations of H2 in synthetic air at room temperature. The highest sensitivity of 75% was measured towards 1% H2 when average size of Au-NPs on NCNTs is 5 nm.