Display omitted •We investigate H2S poisoning process for sensing composite material.•We use XPS spectroscopy and SEM/EDX for chemical analysis.•We compare the properties of the material with chemical response of its components.•We prove the requirement of oxygen to recover the sensing abilities of this material.•We compare the behavior of different types of nanotubes within the sensing material. The poisoning of H2S sensing material based on the mixture of acid-treated carbon nanotubes, CuO and SnO2 was investigated by exposing the material to high doses of H2S (1% in volume) and following the changes spectroscopically. The presence of metal sulfides (CuS and SnS2), sulfates and thiols was confirmed on the surface of this material as the result of H2S poisoning. Further study revealed that leaving this material in air for extended period of time led to reoxidation of metal sulfides back to metal oxides. The formation of thiols and sulfates directly on carbon nanotubes is not reversible under these conditions; however, the extent of the overall surface reaction in this case is substantially lower than that for the composite material.