Abstract An enzyme electrode and a bioelectronic nose (bio-nose) for methyl mercaptan (MM), as one of the malodorous substances were constructed using flavin-containing monooxygenase (FMO). The characteristics of the FMO immobilized electrodes were successfully improved by applying a substrate regeneration cycle with ascorbic acid (AsA) as reducing reagent, thus obtaining the calibration curve against MM solutions from 0.03 to 4.98mmol/l, with 10.0mmol/l AsA. The bio-nose was also fabricated by incorporating the FMO3 immobilized electrode into a reaction cell with both gas and liquid compartments separated by a porous hydrophobic membrane. The device was possible to monitor MM in the gas phase from 1.0 to 4000ppm, with high gas selectivity caused by the FMO3 substrate specificity. As the results of comparison between several kinds of the MM sensors with isoform FMOs, the FMO3 (type 3) immobilized nose was suitable for the measurement of MM vapor because of higher output current than those of other devices.