Acanthopanax koreanum Nakai (Araliaceae) is a medicinal plant indigenous to Korea. The root and stem barks of Acanthopanax species have been used as a tonic and sedative as well as in the treatment of rheumatism and diabetes. In our study, three lignans, eleutheroside E (EE), tortoside A (TA), and syringaresinol (SY), were isolated from the stem and root of A. koreanum in an effort to study the immunomodulating effect. We treated natural killer cells and dendritic cells with lignans (EE, TA, or SY), and analyzed their cytokine (IL-12 and IFN-${gamma}$) secretion. EE, TA, or SY markedly enhanced IL-12 secretion in mouse lymphoid (DC1) and myeloid type (DC2.4) dendritic cells after 48 hr of treatment. There were no significant differences in the cytokine stimulatory effects between EE, TA, or SY. Moreover, treatment of EE, TA, or SY significantly induced IFN-${gamma}$ secretion by human NK cells (NK92MI) confirmed by ELISA assay. This study suggests that lignans from A. koreanum modulate cytokines, and that such modulation may provide the mechanism of action for many of their therapeutic effects.