We examined the effect of stable transfection of dominant negative TβR‐II (dn TβR‐II) cDNA in a human oral carcinoma cell line that contained normal Ras and was growth inhibited by TGF‐β1. Two clonal cell lines containing dn TβR‐II were isolated and compared to the vector‐only control and parent cell line. The treatment of cells with exogenous TGF‐β1 resulted in a decrease in ligand‐induced growth inhibition and loss of c‐myc downregulation in test cells compared to controls; transcriptional activation of certain genes including fra‐1 and collagenase was retained. Cells containing dn TβR‐II grew faster in monolayer culture, expressed less keratin 10 and exhibited increased motility and invasion in vitro compared to control cell lines. Endogenous TGF‐β1 production and the regulation of MMP‐2 and MMP‐9 by TGF‐β1 remained unchanged. After orthotopic transplantation to the floor of the mouth in athymic mice, cells containing dn TβR‐II formed comparable numbers of primary tumours at the site of inoculation as controls but the tumours were less differentiated as demonstrated by the absence of keratin 10 immunostaining. Further, metastatic dissemination to the lungs and lymphatics was more evident in grafts of cells containing dn TβR‐II than controls. Taken together, the results demonstrate that attenuation of TGF‐β signalling through transfection of dn TβR‐II cDNA leads to an enhanced growth rate, a loss of tumour cell differentiation and an increase in migration and invasion, characteristics that corresponded to the development of the metastatic phenotype. © 2004 Wiley‐Liss, Inc.