Room temperature gas-sensitive metal oxides have received growing concern over their long-term stability in recent years. Presently, Pt-SnO.sub.2 composite nanoceramics of 1 wt% Pt have been prepared, and the time dependence of their room temperature hydrogen sensing capability has been carefully studied. A strong variation with time was observed, with the room temperature response to 1% H.sub.2- 20% O.sub.2-N2 decreased by a factor of several dozen after only one week. Heat treatments were found highly effective to activate those aged samples. Their room temperature hydrogen sensing capability was almost completely restored through 10 min heat treatments at temperatures as low as 130 °C. It is proposed that impurity gases in air slowly deposit on Pt in Pt-SnO.sub.2 composite nanoceramics, and the catalytic role of Pt is deactivated by the deposition and then activated after their desorption through heat treatments. These results suggest that periodic mild heat treatments can be a simple and feasible way for some room temperature gas-sensitive metal oxides to maintain a high long-term stability.