Methods: Intravenous administration of Platycodon grandiflorum was performed 2 days before tumor inoculation, then mice were killed 14 days after tumor inoculation, then number of tumor colonies were counted. Methanol extracts of Platycodon grandiflorum was added to colon26-M3.1 carcinoma cells, L5178Y-R lymphoma cells and Hela cells, and then cell growth was counted. To observe the immunomodulating effects of Platycodon grandiflorum, production of IL-6, IL-10, IL-12 and TNF-$alpha$ were measured with ELISA assay and the cell growth of macrophage were also counted. Furthermore, antimetastatic experiment after depletion NK cells by injection of anti-asialo GM1 serum was also administered. Results: Intravenous administration of Platycodon grandiflorum significantly inhibited metastasis of colon26-M3.1 carcinoma cells. In an in vitro cytotoxicity analysis, Platycodon grandiflorum affected tumor cell growth above specific concentration. As compared with control, the production of IL-6, IL-10, IL-12 and TNF-$alpha$ were incresed. And depletion NK cell completly abolished the inhibitory effect of metastasis. Conclusion: Platycodon grandiflorum appears to have considerable activity on immunomodulating effects and inhibit the metastasis of tumor. Further evaluation is needed for settling this.