In this paper we authors studied on Wallach rearrangement reaction of 2,2'-dimethyl azoxybenzene (DMAB) using sulfuric acid, chlorosulfonic acid and some other weak acids as catalysts, and obtained the following results ; (1) We could obtain 4-hydroxy-2,2'-dimethyl azobenzene as a rearrangement product from DMAB in 80% sulfuric acid, under the reaction temperature 80℃ and time 30 minutes. The yield of 64% obtained in this experiment was better than that of 31% at which Gore et al had obtained the product. (2) In case where chlorosulfonic acid was used in the rearrangement, It is a contradictory results against Wallach rearrangement by ordinary acid catalysts. The yield of o-isomer in the reaction products was higher than that of p-isomer in rearrangement. (3) We also tried Wallach rearrangement by weak acids for the first taime, and obtained p-isomer at yield of max. 38.8% with trichloroacetic acid in acetic anhydride
