Cordycepin was purified from a mushroom, Cordyceps militaris, and its effect on Th1 and Th2 cytokines was examined. The level of cytokine induction in mouse splenocytes was estimated after co-inoculation of purified cordycepin and LPS. When $5{mu}g/ml$ of purified cordycepin was exposed to mouse splenocytes for 72 h, the level of a Th1 cytokine IL-12 increased by 2.9-fold. The addition of the purified cordycepin to splenocytes also increased the level of Th2 cytokines, IL-4 and IL-10, by 1.9- and 1.8-fold, respectively. Therefore, cordycepin increases the cytokine levels and may contribute to the up-regulation of cellular and humoral immunity.