Deoxygenation of 1, 2-dimethylbenzimidazole 3-oxide (I) proceeded by treatment with phosphorus trichloride, sulfur dioxide, sodium hydrogensulfite and sodium borohydride besides by catalytic reduction with Raney nickel. The methyl group at C-2 of I seemed less reactive than that of the parent base and did not condense with benzaldehyde, p-dimethylaminonitrosobenzene or p-nitrobenzenediazonium chloride. However, I reacted with dimethyl oxalate in the presence of alkali to give 2-methoxalylmethyl-1-methylbenzimidazole 3-oxide in good yield. The reactions of I with acetic anhydride, benzoyl chloride, phosphoryl chloride, tosyl chloride, tosyl chloride-pyridine, potassium cyanide-benzoyl chloride, methyl cyanoacetate-acetic anhydride, phenyl isocyanate, phenyl isocyanide and isoamyl nitrite-sodium amide were examined. By these reactions, 2-substituted methyl-1-methylbenzimidazole and/or 6-substituted 1, 2-dimethylbenzimidazole were obtained. As a co-ordination compound, the boron trifluoride complex of I was obtained.