It is well known that immune response decreases with aging. Salidroside (SDS), an antioxidant component isolated from the traditional Chinese medicine roseroot Rhodiola rosea, has been demonstrated to possess potent anti-aging and health-promoting activities. However, the mechanism underlying these activities is poorly understood. In this study, we clearly demonstrated that (1) dietary intake of SDS induced a considerable increase in total T cells (CD3(+)) and T helper cells (CD4(+)) in aged (21 months old) Wistar male rats; (2) SDS supplementation significantly increased the DTH response, a T cell-mediated immune response, in aged rats; and (3) SDS supplementation remarkably promoted the production of total anti-KLH IgG, anti-KLH IgG1, and anti-KLH IgG2α in aged rats without disturbing immune homeostasis. These indicate that SDS is able to counteract immunosenescence, thereby resulting in rejuvenation. Practically, SDS may be used to help the elderly to generate an improved response to vaccine with stronger humoral and cell-mediated immune responses.