Abstract: A SnCl₂ solution was used to prepare SnO₂-coated multi-walled carbon nanotubes (SnO₂/MWCNTs), and their hydrogen sensing properties at room temperature was studied. SEM and TEM observations indicate that SnO₂ nanoparticles with a size of 5 nm are uniformly coated on the MWCNTs, forming a continuous SnO₂ coating. The SnO₂/MWCNTs are sensitive to 10-4 hydrogen at room temperature. During the sensing measurement at room temperature for 10-3 hydrogen mixed with argon gas, the current change with gas concentration is reversed after the mixed gas is switched to air. This can be ascribed to the reaction between O₂ in air and residual H₂ around the SnO₂/MWCNTs to form adsorbed H₂O and the subsequent desorption of H₂O by substitution adsorption of O₂ in air. The H₂O adsorption may lead to a decrease of the electric resistance of SnO₂/MWCNTs and thus an increase of current measured. The reversal of current implies that the SnO₂/MWCNTs may possess a good sensitivity to humidity at room temperature.