Gas sensors based on tin dioxide-carbon nanotube composite films were fabricated by a simple inexpensive sol-gel spin-coating method using PEG400 as a solvent. Nanostructured copper was coated on CNTs/SnO 2 film, and then copper was transformed into copper oxide at 250°C. Resistivity of the final composite films is highly sensitive to the presence of H 2 S, which became easily attached or detached at room temperature. The response and recovery time of the sensor are 4 min and 10 min, and the value of sensitivity is 4.41, respectively. Meanwhile, the CNTs/SnO 2 /CuO sensor also has low detection limit, high selectivity toward H 2 S, and stable performance with different concentrations of H 2 S.