The purpose of this research was to investigate the immunoregulatory effect, apoptosis of L 1210 leukemia cells of Comus officinalis Sieb.et Zucc. The proliferation of cultured splenocytes and thymocytes were enhanced by the addition of SSY. Splenic, thymic and mesenteric lymph node-T lymphocytes, especially TH cells was significantly increased in SSY-administered (p.o. for 7 days) mice. SSY treatment induced the apoptosis of L1210 mouse leukemia cells. In addition, SSY accelerated the phagocytic activity and nitric oxide production in peritoneal macrophages. These results suggest that SSY have an immuno-regulatory property and anti-cancer effect.