Abstract: Mesenchymal stem cells (MSC) not only exhibit a marked tropism for tumors, but also exert antitumorigenic activity or as an emerging vectors to express foreign genescontinuously and efficiently within the tumor microenvironment, suppress tumor’s growth and metastasis. Conversely, MSC can accelerate tumor development through promoting tumor stroma remodeling and tumor vascular formation, inhibiting tumor lacal immune and changing tumor phenotype. The reason for this discrepancy may be attributable to different sources of MSC, the heterogeneity of MSC, differences in tumor microenviroment, or another factor that is not yet appreciated.