Human mesenchymal stem cells (hMSCs) have been applied in a variety of therapies recently. However, the role of MSCs in tumor progression remains largely elusive. Some studies demonstrated that MSCs can promote tumor growth, while others had opposite results. Therefore, the lack of evidence about the effect of MSCs on tumor cells impedes its further use.In the current study, hMSCs from amniotic membrane (hAMSCs) and umbilical cord (hUCMSCs) were used to evaluate the effects of MSCs on tumor development in vitro and in vivo. Two different animal models based on subcutaneous xenograft bearing nude mice and a murine experimental metastatic model were established for in vivo study. Moreover, cytokines regulated by MSCs co-cultured with cancer cells SPC-A-1 were also analyzed by cytokine array.Our results indicated that hUCMSCs not only did not promote proliferation in cancer cells, but also inhibited migration. In addition, they inhibited tube formation in human umbilical vein endothelial cells (HUVECs). Although hAMSCs also showed inhibitory effects on cancer cell motility, the proliferation of cancer cells was indeed enhanced. The in vivo data revealed that hUCMSCs did not promote tumor progression in lung adenocarcinoma and gastric carcinoma xenografts. Nevertheless, hAMSCs could do. The results from murine experimental metastatic model also demonstrated that neither hUCMSCs nor hAMSCs significantly enhanced the lung metastasis. The data from cytokine array showed that 11 inflammatory factors, 8 growth factors and 11 chemokines were remarkably secreted and changed.In view of the data from in vitro and in vivo studies, the exploitation of hUCMSCs in new therapeutic strategies should be safe compared to hAMSCs under malignant conditions. Moreover, this is the first report to systematically elucidate the possible molecular mechanisms involved in UCMSC- and AMSC-affected tumor growth and metastasis.