The effectiveness of electrolyzed cathode water (ECW) prepared by the electrolysis of NaCl (100 mg/L) aqueous solution was examined in inhibiting the oxidation of some reductants which are widely used in food and biochemical researches. When L-ascorbic acid dissolved in the ECW or sodium hydroxide aqueous solution was incubated for 30 min, the remaining ratio of L-ascorbic acid dissolved in ECW was 1.21-1.24 times higher than that dissolved in sodium hydroxide aqueous solution. The oxidation-reduction potential of ECW decreased with hydrogen gas generation after electrolysis, namely the reducing potency of ECW became higher. Thus the oxidation of L-ascorbic acid was considered to be depressed by such a high reducing potency. The decreased level of dissolved oxygen in ECW by the hydrogen gas generation related to its antioxidative activity. The oxidation of dithiothreitol, 2-mercaptoethanol and α-tocopherol were also depressed in the ECW. It was confirmed that the reducing potency and low dissolved oxygen concentration were responsible for the antioxidative activities of ECW toward dithiothreitol and 2-mercaptoethanol. However, unlike the cases of these hydrophilic reductants, the depressing effect of ECW on the oxidation toward α-tocopherol, a lipophilic reluctant, could not be explained only by the reducing potency and low dissolved oxygen, probably because it existed as an emulsion in the presence of the surfactant, sodium dodecyl sulfate.