An amperometric biosensor for sulfite determination, based on the incorporation of sulfite oxidasen (SOD) into a polypyrrole film by galvanostatic formation, has been successfully developed. The use of the biosensor involves the application of a constant potential of –700 mV, which promotes oxgen reduction as the predominant reaction. The optimum analytical conditions for the biosensor were 0.1 M phosphate buffer with 0.5 M KC1. pH 7.0, and a platinum disk electrode. The response of the biosensor to sulfite was linear from 0 to 80 mg/L, and the minimum detectable amount was found to be 5 mg/L. Usual interferants in sulfite determination such as ascorbic acid, sodium nitrite, and sodium sulfate did not interfere with the biosensor. The excellent resproducibility of the sulfite response with 4 hours of repeated use provides the basis for the construction of a disposable or renewable biosensor for sulfite determination.