We here demonstrate the evidence of increased anti-tumor and immunostimulating activities of crude extracts (GAL) from Galium. aparine L. In experimental lung metastasis of colon26-M3.1 carcinoma or B16-BL6 melanoma cells, prophylactically intravenous (i.v) administration of GAL significantly inhibited lung metastasis in a dose-dependant manner. In an in vitro cytotoxicity analysis, GAL at the concentration up to $500;{mu}g/ml$ did not affect the growth of B16-BL6 melanoma cells. In contrast, GAL showed the enhancement of splenocyte proliferating activity in a dose-dependent manner. Peritoneal macrophages stimulated with GAL produced various cytokines such as $1L-1{eta},;TNF-{alpha},;IFN-{gamma}$ and IL-12. These data suggest that GAL has an antitumor activity to inhibit tumor metastasis, and its antitumor effects is associated with activation of nonspecific immnune related cells.