Objectives The purpose of this study was to investigate the effect of Yongyukjowitang(YJT) distillate on the immune activity of spleen cells of aged SD rats. Methods Spleen cells from 10w, 52w, 72w old rats were stimulated with Concanavalin A(Con A) and treated with Vitamin C(Vit.C) or Yongyukjowitang distillate(YJT). After 24 hours, levels of IL-2, IL-4, IL-10, IFN-${gamma}$ were measured using ELISA in spleen cells. Results and Conclusions 1. The concentration of IL-2, IL-4 in spleen cells of 52 weeks old SD rats(YJT group) significantly decreased in comparison with ConA group. 2. The concentration of IFN-${gamma}$ in spleen cells of 72 weeks old SD rats significantly increased in comparison with 10 weeks old SD rats(NT group), but decreased in comparison with 10 weeks old SD rats(YJT group). These results suggest that Yongyukjowitang distillate has an effect on the immune activity of spleen cells of aged SD rats.