The objective of the present invention is to provide an antioxidation method and antioxidant-functioning water that can anticipate high benchmarks of safety on the antioxidation subject such as the human body and reduced environmental burden. An antioxidation method and antioxidant-functioning water that can transform or maintain an antioxidation subject, which is in an oxidation state due to a deficiency of electrons or needs to be protected from oxidation, into a reduced state where electrons are filled by promoting the breaking reaction of molecular hydrogen used as a substrate included in the hydrogen-dissolved water into a product of active hydrogen through a process employing a catalyst, which is a precious metal colloid or a hydrogen oxidation/reduction enzyme (except for those already existing in a living organism), on the hydrogen-dissolved water.