We present results on the development of nanocomposite NiO:Au thin-film hydrogen sensors, which are able to detect hydrogen concentrations as low as 2 ppm in air, operating at low temperatures in the range 125 -150 o C. Thin NiO films were sputterdeposited on oxidized silicon substrates. The structural, morphological, and nanomechanical properties of the films were investigated with respect to postdeposition annealing. Au nanoparticles were added on the NiO surface via pulsed laser deposition and the films were tested as hydrogen sensors before and after Au deposition. The performance of the NiO films as hydrogen sensors improved significantly in the presence of Au nanoparticles on the surface. The detection limit (lowest detectable hydrogen concentration) decreased by two orders of magnitude, while the response time also decreased by a factor of three.produced and distributed in the near future for passenger vehicles and aircrafts, as well as a city gas. Dangers associated with hydrogen include high permeability through many materials, flammability (lowest explosion limit is 40,000 ppm in air), and lack of odor, taste, and color, which renders it undetectable by human senses [1].Therefore, smart hydrogen sensors with high sensitivity and low power consumption are essential in order to achieve safe and efficient processing of hydrogen on a massive scale.Gas sensor technologies vary depending on the mechanism of operation, such as resistive, electrochemical, catalytic, optical, and mechanical, among others. Each technology presents important advantages and certain disadvantages, depending on the application. Resistive gas sensors detect changes in the electrical resistance of a material in the presence of an analyte gas [1], [2]. The advantages of resistive gas sensors include low cost, high sensitivity, and wide operating temperature range.Metal-oxide thin films have been successfully employed as resistive sensors due to their electrical response in the presence of a reducing or oxidizing gas. Metal oxides such as SnO 2 [3], ZnO [4], and TiO 2 [5], among others, have shown very good hydrogen sensing properties, such as high sensitivity, fast response, and long-term stability, combined with low-cost and flexible production, as well as simplicity in their use. One of the drawbacks of metal-oxide sensors, is that they have to be heated