We studied how consumption of vitamin C (VC) affects the oxidative stress regulation system. SMP30/GNL knockout mice (males, n = 33), which cannot synthesize VC, were randomly divided into three groups: the VC 100 Group consuming 1.5 g/L VC, the VC 2.5 Group consuming 0.0375 g/L VC, and the VC 0 Group consuming 0 g/L VC. To examine the oxidative stress regulation system, the reactive oxygen metabolites (d-ROM test) and biological anti-oxidant potential (BAP test) values were measured, and the BAP/d-ROM ratio was calculated. We obtained measurements at the beginning of the study (5 weeks old: baseline) and after VC consumption for 9 weeks (14 weeks old: 9 wk). For the plasma VC concentration, plasma reduced (ascorbic acid (AA)) and plasma oxidized (dehydroascorbic acid (DHA)) were measured at 9 wk, and the total VC (AA + DHA: total) concentration was calculated. Compared to the other groups at 9 wk, the VC 100 Group showed a significantly lower value for the d-ROM test, a significantly higher value for the BAP/d-ROM ratio, no significant difference in the BAP test, and a significantly lower senescence grading score. The VC 100 Group showed a significantly higher total VC concentration compared with the other groups. Differences in consumption of VC caused a change in the d-ROM test, the BAP/d-ROM ratio, and the plasma VC concentration.