The alkylation of hydroxy-benzenes, such as methylhydroquinone, phenylhydroquinone, and tert-butylhydroquinone, was studied utilizing isobutylene or tert-butanol as the alkylating agent to obtain 2,5-substi-tuted hydroquinones. The alkylation was carried out in the presence of acid catalysts such as Amberlyst-15 or 70% sulfuric acid in a batch reactor. As reactiion solvent, a mixture of cyclohexane and 2-heptanone or ethyl acetate was found to be a good solvent system. The cation exchange resin catalyst Amberlyst-15 offered better selectivity to 2.5-substituted hydroquinones than 70% sulfuric acid. a steric hindrance imposed of fixed protons in solid acid catalyst such as Ambr\erlyst-15 caused higher selectivity toward less-hindered position. It was also found that the selectivity was affected by groups substituted on hydroquinones; the selectivity of 2,5-substituted hydroquinones was in the descending order of tert-butyl, phenyl, and methyl-hydroquinones. The separation of 2.5-substituted hydroquinones from the reaction mixture was successfully accomplished by utilizing extraction and crystallization.