To provide a method for efficiently and industrially deuterating the benzyl position of a --O-benzyl group formed by introducing a benzyl group, a benzyloxymethyl group and the like as a protecting group. The deuteration method for the benzyl position of a --O-benzyl group of a compound having the --O-benzyl group which may have a substituent, comprising reacting the compound with a heavy hydrogen source in the coexistence of a palladium/carbon-ethylenediamine complex and hydrogen.