A bioelectronic nose (Bio-nose) for methyl mercaptan (MM) in the gas-phase was constructed a flavin-containing monooxygenase 3 (FMO3) and a reaction cell with both gas- and liquid-compartments separated by a porous hydrophobic membrane. The FMO immobilized electrode was calibrated against MM solutions from 0.03 to 4.98 mmol/l since the characteristics of the FMO3 immobilized electrode was improved by applying a substrate regeneration cycle with ascorbic acid as reducing reagent, The bio-nose with the FMO3 immobilized membrane could be used to measure MIA in the gas phase, and possessed high selectivity being attribute to the FMO3 substrate specificity, continuous measurability and good reproducibility.