Methanolic extract of Emilia sonchifolia (Compositae), a folklore medicinal plant, was found to be cytotoxic to Daltons lymphoma (DL), Ehrlich ascites carcinoma (EAC) and mouse lung fibroblast (L-929) cells, but not toxic to normal human lymphocytes, under in vitro conditions. Oral administration of the extract (100 mg/kg, b. wt) to mice reduced the development of both solid and ascites tumors and increased the life span of these tumor bearing mice. Further, the extract inhibited DNA synthesis as judged from a reduction in tritiated thymidine incorporation into DL cells under in vitro conditions.