An optical sensing method was proposed for monitoring SO 2 gas in the environment based on photoluminescent quenching of lightly oxidized porous silicon.After electrochemica,etching and light oxidizing by UV light,the porous silicon film showed high sensitive characteristic to SO 2 gas.The principle of this method was analyzed,the film properties were studized by SEM and luminescence spectrometer.The reversible photoluminescent quenching of lightly oxidized porous silicon can be observeded so long as contacting with SO 2 gas.The experimental results were in good accordac e with the principle.