It has been found that thiamine-protein complexes and unbound disulfide-type thiamines are produced by the reaction of thiamine or O-benzoyl thiamine (OBT) with iodine oxidized egg albumin at pH 7.3 or 9.0,37℃ for 60 minutes. The complexes were not separated into their components by means of zone-electrophoresis, dialysis and metaphosphoric acid deproteinization, but free thiamine was liberated by the reduction with sodium thiosulfate or cysteine. From these results, the complexes were comfirmed to be protein-thiamine mixed disulfides which were produced by the reaction of thiol-type thiamine with S-S group of the oxidized protein. By the reaction at pH 9.0 larger amounts of the combined thiamines were produced than those at pH 7.3. The result was considered due to a higher concentration of the thiol-type thiamines at pH 9.0. OBT showed a higher reactivity with the oxidized protein than that of thiamine. An optimal amout of iodine for the oxidation of protein was about 5 molar-equivalents of the protein.