We studied effects of Samreungjeon water extract (SE) on the proliferation of transplanted-L1210 cells to mice. Samreungjeon is composed of Scirpi Tuber, Zedoariae Rhizoma, Aurantii immaturi Pericarpium, Pinelliae Tuber and Hordei Fructus Germinatus. When SE (500 mg/kg) was administered orally once a day for 7 days after transplantation of L1210 cells to mice, the proliferation of transplanted-L1210 cells was decreased and DNA fragmentation of transplanted-L1210 cells was induced. Also, DNA fragmentation of L1210 cells was enhanced by co-culture with the peritoneal macrophages obtained from SE-administered mice and was partly inhibited by L-NMMA in vitro. SE enhanced the production of nitric oxide from murine peritoneal macrophages in vitro and in vivo. These results suggest that SE partly induces apoptosis of transplanted-L1210 cells via production of nitric oxide from macrophages.