Objective　We investigated the antioxidant and stress-mitigating properties of a novel antioxidant, 3,5-dihydroxy-4-methoxybenzyl alcohol（DHMBA）, isolated from the soft tissue of Pacific oyster（Crassostrea gigas）, in a mouse model of oxidative stress.
Methods　Two kinds of extracts were prepared from the soft tissue of Pacific oysters: one contained DHMBA（24.3μg/mL）and the other was free from DHMBA. Thirty male Slc: ICR mice were individually housed for 42 days to produce the isolated oxidative stress mice. The animals were divided into 3 groups and orally administered with water, the DHMBA-containing extract, and the DHMBA-free extract for 8 days. We collected blood, liver, kidney including adrenal gland, pancreas, and spleen from those mice and measured the levels of malondialdehyde in each organ, 8-hydroxy-2'-deoxyguanosine（8-OHdG）in kidneys and corticosterone in plasma.
Results　The animal group administered with the DHMBA-containing oyster extract showed significantly lower levels of malondialdehyde in each organ, 8-OHdG in the kidneys, and plasma corticosterone than those with water or the DHMBA-free extract.
Conclusions　DHMBA in the oyster extract exhibited lipid antioxidant activity in each organ, fatigue-mitigating activity via DNA antioxidant effect on the kidneys, and stress-mitigating activity via a reduction in plasma corticosterone levels.