A ⁸⁵Kr irradiation equipment has been devised for chemical reaction in the liquid phase. Irradiation is achieved by circulating the ⁸⁵Kr gas in a reaction system, where the ⁸⁵Kr gas forms bubbles in the liquid reactant. The dosimetry is carried out for the reaction system using aqueous solutions of methylene blue. The observed relationship between the absorbed dose rate in the reactant and the fractional void in the reaction vessel agrees well with the theoretically obtained relationship.