The subject of the present invention is to provide a method for deuteration, which can obtain a compound having an aromatic ring and/or a heterocyclic ring at an improved deuteration ratio. The present invention relates to a method for deuteration of a compound having an aromatic ring and/or a heterocyclic ring, comprising reacting the compound having an aromatic ring and/or a heterocyclic ring with a heavy hydrogen source in the presence of an activated mixed catalyst of not less than two kinds of catalysts selected from among a palladium catalyst, a platinum catalyst, a rhodium catalyst, an iridium catalyst, a ruthenium catalyst, a nickel catalyst and a cobalt catalyst.