Purpose: This study was designed to investigate the antimetastatic and immunomodulating effects of extracts of Ulmus davidiana extracts(U. D. Ex.). Methods: Antimetastatic experiments were conducted in vitro and in vivo by using colon 26-M3.1 carcinoma, L5178Y-R lymphoma cell and Hela cell. To observe the immunomodulating effects of U. D. Ex., we measured IL-6, IL-10, IL-12 and TNF-$alpha$ from peritoneal macrophages. And we evaluated the activation of NK cell by using anti-asialo-GM1 serum. Results: We found that the administration of U. D. Ex. significantly inhibited tumor metastasis in vivo. In vitro cytotoxicity analysis, cell growth are closer to 100% in case of Colon 26-M3.1 carcinoma, L5178Y-R lymphoma cell and Hela cell at low concentration. In case of macrophage, cell proliferation is closer to 100% less than $250{mu}g/ml$ of U. D. Ex.. The level of cytokine such as IL-6, IL-10, IL-12 which stimulates U. D. Ex. was increased in dose-dependent manner compared to the control group. In case of TNF-$alpha$, the level was increased at concentration of $1,000{mu}g/ml$. The depletion of NK cells by anti-asialo GM1 serum partly abolished the inhibitory effect of U. D. Ex. on tumor metastasis. Conclusion: Ulmus davidiana appears to have considerable activity on the anti-metastasis by activation the immune system.