Icariin (ICA) is a kind of new biological respone modifier(BRM) and differentiational agent. In order to further elucidate the reversion of malignant phenotypes of tumor cells and the mechanism of its action, highly metastatic human lung cancer cells(PG) were treated with ICA in vitro. In this study, MTT assay, radioimmune assay, flow cytometry(FCM) and invasion assay were used. The results showed that ICA could influence the distribution of PG cells cycle and reduce S phase. Moreover, ICA increased the level of cAMP in PG cells, reduced the level of cGMP and increased the cAMP/cGMP ratio. On the other hand, ICA decreased PG cells adhesive ratio to laminin substrate and decreased the ability of invasion or migration. These data demonstrate that ICA maybe a kind of effective anticancer drug.