Chemoresistive H2S sensors using various oxide nanoparticles were prepared and heat-treated at 600 degrees C in an effort to define halitosis in human breath. WO3, ZnO, and SnO2 were tested as sensing materials, among which WO3 showed the highest stability to H2S. XPS analysis showed a metal sulfate peak on the surface of ZnO and SnO2, which causes a recovery problem after 2 ppm H2S exposure. On the contrary, the WO3 sensor showed a stable signal in long-term operation in the presence of H2S gas. WO3 gas sensors decorated with various catalytic metals were fabricated to investigate their sensing properties in the 0.2-5 ppm H2S range with 80% relative humidity (RH). A 0.03 wt% Au-doped WO3 sensor exhibited excellent H2S sensitivity (R-air/R-gas = 12.40 at 2 ppm) toward H2S, whereas pure WO3 showed a sensitivity of 4.85 with negligible interference from the volatile organic compounds (VOCs).