An infrared optical fiber made of As2S3glass has been applied for remote sensing of hydrocarbon gases. The fiber has enabled a transmission of the radiation at 3.39‐&mgr;m wavelength, where hydrocarbon molecules have strong absorption bands. Using a 3.39‐&mgr;m He‐Ne laser as a light source, an effective remote sensing system has been established. A detection limit of the gas concentration is ∼300 ppm for CH4gas, which is ∼0.6% of the lower explosion limit. The system is also expected as a pressure monitor since it is highly sensitive to the gas pressure.