This paper reviews evidence for the immune-enhancing effects of prebiotics. The influence of inulin and oligofructose on the immune functions and the structure of immune peripheral organs in male Wistar rats was investigated after 4 months feeding. Rats fed isocaloric purified diets contained 10% inulin or oligofructose. The rats of control group had no feeding any prebiotics. The enlargement of a number of T-cells and increasing of major histocompatibility complex (MHC-II) molecule on the surface of an antigen-presenting cells of spleen, mesenteric lymph nodes, thymus was noted. The increasing of content interleukin-2 and interleukin-4 in blood was noted in rats fed inulin and oligofructose. The increased activity of peritoneal macrophages was confirmed by enhance superoxid anion production and phagocytosis. The dietary prebiotics do not influence on the apoptosis of immunocytes. The immune-enhancing effects of prebiotics was confirmed by morphological investigation of peripheral lymphoid organs.