Surface acoustic wave (SAW) sensors based on sol–gel processed porous and nanoparticulate CuO films were explored for H2S detection operated at room temperature. The SAW sensor showed a negative frequency shift when exposed to H2S gas, due to the mass loading effect on the sensitive CuO film. It has a high sensitivity of H2S, a detection limit of 500 ppb and a good selectivity to H2S gas compared with H2, C2H5OH, acetone, NH3, CO, NO, NO2 gases. Relative humidity (RH) was identified to have a critical influence on the sensing performance of the sensor. The responses became much faster and stronger with the increase of RH. The significant enhancement in the sensing performance is attributed to that the chemical reaction between H2S and CuO is hindered and the physical adsorption of CuO to H2S is enhanced.