The chemical constituents of root bark of Acanthopanax sessiliflorum Seemann(Araliaceae) which is distributed in southern region of Korea are studied. The five kinds of chemical constituents are isolated from MeOH extract of root bark by column fractionation and purified by recrystallization. Substance $I{sim}III$ were identified as stigmasterol, ${eta}-sitosterol$ and campesterol. Substance IV is suggested as a lignan substance based on chemical and spectral discussions. The molecular formula of substance $V;show;C_{20}H_{18}O_6$ and its melting point is $120.5{sim}121.5^{circ}$. Due to the spectral data, it is confirmed that substance V is a (+) sesamin of lignan.