Ovomucoid (OMC) is the most prominent allergen causing egg allergy, and contains disulfide (S-S) bonds that may be responsible for its allergic action. As S-S bonds may be reduced during electrolysis on the cathode side, this study was undertaken to evaluate modulation of the allergic action of OMC after electrolysis. A current of 30 mA/cm2 was applied. The allergic action was evaluated by means of skin prick tests (SPT) with egg-allergic patients, and the modification of OMC was examined by MALDI-ToF-MS after tryptic digestion. The total free SH groups in 1% OMC solution were increased on the cathode sides after electrolysis for 30 minutes (14.8 nmol/ml) as against those of untreated OMC (1.2 nmol/ml) and OMC on the anode side (2.8 nmol/ml). Significant mitigation of the wheal reactions by 22% were observed in the SPT with OMC on the cathode when compared with those for untreated OMC, however, the wheal reactions on the anode side did not differ from those for untreated OMC. The MALDI-ToF-MS results for untreated OMC or OMC on the anode side showed two peptide fragments suspecting potential S-S bonds (residues 63L-85S, 358A-379R) but, on the contrary, OMC on the cathode side did not give the fragments suspecting potential S-S bonds. The allergic action of OMC can be mitigated during electrolysis on the cathode side, being simultaneously formed intramolecular free SH groups. This study was supported by the Kieikai, Tokyo, and a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science.