Objectives : The purpose of this study is to investigate the effect of oral administration of Yongyukjowi-tang(YJT) on the immune activity in aged Sprague-Dawley rat(SD rat). Methods : SD rats were divided into three groups: Yongyukjowi-tang groups(YJT groups), distilled water groups(control groups) and Vitamin C groups(positive control groups) which were administered an oral dose(1ml/1day) to 6, 48 and 68 weeks old SD rats for four weeks. After four weeks, the number of total leukocyte, CD3+, CD4+, CD8+, and the level of cytokine (IL-2, IL-4, IL-10, IFN-${gamma}$) were measured in spleen tissue of each SD rats. Results and Conclusions : 1) The number of total leukocyte significantly increased in 52 weeks old YJT group and 72 weeks old YJT group in comparison with those of the control group. 2) The number of CD3+ cell significantly increased in 72 weeks old YJT group in comparison with those of the control group and the positive control group. 3) The number of CD8+ cell significantly increased in 52 weeks old YJT group in comparison with those of the control group. 4) The level of IL-2 significantly increased in 72 weeks old YJT group in comparison with those of the control group and the positive control group. 5) The level of IL-4 significantly increased in 52 weeks old YJT group in comparison with those of the positive control group. These results suggest that oral administration of YJT has an effect on increase of immune activity in aged rat.