Oxygen (O2) is a prerequisite for cellular respiration in aerobic organisms but also elicits toxicity. To understand how animals cope with the ambivalent physiological nature of O2, it is critical to elucidate the neuronal and molecular mechanisms responsible for O2 sensing. We have conducted systematic evaluation of TRP cation channels using reactive disulfides with different redox potentials to reveal the capability of a TRP channel to sense O2. O2 sensing is based upon disparate processes: while prolyl hydroxylases (PHDs) exert O2-dependent inhibition on the TRP channel activity in normoxia, direct O2 action overrides the inhibition via the prominent sensitivity of the TRP channel to cysteine-mediated oxidation in hyperoxia. Surprisingly, the TRP channel is activated through relief from the same PHD-mediated inhibition in hypoxia. In mice, gene disruption of the O2-sensitive TRP channel abolishes hyperoxia- and hypoxia-induced cationic currents in vagal and sensory neurons, and impedes enhancement of in vivo discharges induced by hyperoxia and hypoxia in vagus, which is known to innervate the trachea and lung. The results suggest a novel O2-sensing mechanism mediated by a TRP channel in vagus. The current study makes a significant contribution to understanding the biology and medicine in terms of toxicity of O2, which is among the most fundamental elements essential for a wide variety of biological processes in aerobic organisms. Considering the physiological importance of TRPA1, defects of TRPA1 should be associated with respiratory and sensory disorders and diseases. TRPA1 will be an important functional marker for certain diseases and an interesting target of drug invention.