Pd nanoparticles (NPs) were successfully functionalized on the surfaces of single-walled carbon nanotubes (SWNTs) by dendrimer-mediated synthesis. The hydrogen sensing properties of the Pd NPs functionalized SWNTs were investigated. Pd NPs-dendrimer-SWNTs sensors show much better speeds and superior recovery rates but lower sensitivity compared toPd NPs-functionalized SWNTs directly fabricated due to the existence of dendrimers. Pyrolysis of the dendrimers by heat treatment resulted in afast response time and high sensitivity owing to the reduced length of the dendrimers. Theseresults demonstrate that the heat treatment of dendrimers in Pd NPs-dendrimer-SWNTs sensors can enable significant electrical conductance modulation upon exposure to extremely low concentrations (10 ppm) of hydrogen gas (H2) in air.