2-O-${eta}$-D-Glucopyranosyl-L-ascorbic acid (AA-$2{eta}G$) is a natural derivative of vitamin C (Lascorbic acid, AA) isolated from Goji berry (Lycium barbarum L.) fruit. We evaluated the antioxidant activities of AA-$2{eta}G$ and AA using in vitro and in vivo model systems. In vitro radical scavenging assays demonstrated that AA-$2{eta}G$ was capable of scavenging 1,1-diphenyl-2-picryl-hydrazyl and hydroxyl peroxide and inhibiting $H_2O_2$-induced hemolysis better than AA. AA-$2{eta}G$ and AA had similar hydroxyl radical scavenging capabilities, but AA-$2{eta}G$ was incapable of scavenging superoxide anion radicals, and its capacity to scavenge nitrite ($NO_2{^-}$) was lower than that of AA. The overall in vitro reduction capability of AA-$2{eta}G$ was also significantly lower than that of AA. Moreover, in vivo studies demonstrated that AA-$2{eta}G$ was capable of protecting the liver against carbon tetrachloride-induced acute liver injury in mice. These results suggest that AA-$2{eta}G$ is an important antioxidant component of Goji berry fruit, which may share similar but distinct antioxidant mechanistic properties with AA. This study furthers our understanding of the mechanisms of Goji berry fruit pharmacological activities on antiaging and antitumor properties as a traditional medicine and dietary supplement.