A nanostructured sensor based on double wall carbon nanotubes (DWNTs) was fabricated and assessed for hydrogen gas detection. DWNT networks were used as an active substrate material evaporated with layers of palladium nanoparticles of three thicknesses 1, 3 and 6 nm. The electrical resistance change of nanosensor with hydrogen gas exposure in compressed air at room temperature was monitored. The nanostructures were characterized using high resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM). Hydrogen concentrations as low as 0.05 vol% (500 ppm) can be detected at room temperature. Sensitivity values as high as 65% and response times of about 3 seconds were obtained. The results indicate that DWNT- based sensors exhibit comparable performance as that for SWNT-based high performance hydrogen sensors, but with potential improvement in mechanical and thermal resistance associated with the double layer structure. © 2009 SPIE.