Migration of tumor cells is a crucial step in tumor invasion and metastasis. Here we provide evidence that aquaporin expression is involved in tumor cell migration. RT-PCR, immunofluorescence and Western blot analysis demonstrated the AQP1 protein expression on the plasma membrane of SMMC-7221 human hepatoma cells. SMMC-7221 cell clones with high (SMMC-7221hPf) and low (SMMC-7221lPf) water permeability were identified by functional assays with corresponding high and low AQP1 expression. Cell migration rate was remarkably higher in SMMC-7221hPf cells than SMMC-7221l Pf cells, assessed by Boyden chamber and wound healing assays, whereas cell growth and adhesion were not different. Adenovirus-mediated AQP1 expression in SMMC-7221lPf cells increased their water permeability and migration rate. These results provide the first evidence that aquaporin-mediated membrane water permeability enhances tumor cell migration and may be associated with tumor invasion and metastasis.