Acanthopanax sessiliflorus, a plant mainly found in Korea, Japan, and China, has been used as a traditional medicine due to the bioactivities of some plant compounds. The antioxidant activity of A. sessiliflorus root in vivo and the anti-aging effect using Caenorhabditis elegans were studied. Pre-treatment with an A. sessiliflorus root extract significantly (p < 0.05) increased resistance to oxidative stress and induced increased survival after heat shock and ultraviolet irradiation treatment, compared with controls. A lifespan assay revealed that both the mean and maximum lifespans were significantly (p < 0.05) extended due to A. sessiliflorus root extracts, compared with controls. The lifespan extension was not accompanied by reduced reproduction, unlike other long-lived mutants. A. sessiliflorus root extracts also protected worms against human beta-amyloid-induced toxicity. A. sessiliflorus root extracts can confer increased resistance to environmental stresses and modulate the aging process in C. elegans.