Abstract The properties of SnO2–MoO3 ceramic sensors for CH4 and CO detection and structural features of sensitive layers, containing different concentrations of Sn and Mo, have been studied. The sensitive layers were obtained by means of the sol–gel method—from tin hydroxide sols, stabilised with polyvinyl alcohol (PVA), with Mo6+ added. The structure of the ceramic layer corresponds to Mo6+ in SnO2 substitution solid solution (up to 25 at.% Mo) at all Mo6+ concentrations in sols. Mo5+ stabilises in SnO2 interstitial positions. At definite ratios of components and operating currents, SnO2–MoO3 sensors can selectively detect CO in CO+CH4 mixtures.