Norcantharidin (NCTD), a potential anti-cancer drug, is the demethylated analog of cantharidin isolated from blister beetles. The present study investigated the effect of NCTD on tumor invasion and metastasis. A cytotoxicity assay of NCTD in CT26 colorectal adenocarcinoma cells showed a dose- and time-dependent decrease in cell viability. NCTD (50 microM)-treated CT26 cells not only showed an inhibited cell invasion of 65.6%, but also decreased the activity of matrix metalloproteinase-2 and -9. NCTD decreased the adhesive ability of CT26 cells in a dose-dependent manner. At a concentration of 100 microM, NCTD showed a down-expression of several cadherin-catenin adhesion molecules, including Desmoglein, N-cadherin, and alpha- and beta-catenin, while there were no obvious changes in E-cadherin and gamma-catenin. Intraperitoneal injection of NCTD (2 mg/kg/day) in BALB/c mice reduced both the pulmonary metastatic capacity of CT26 cells and prolonged the survival day of the mice. These results demonstrated that it was effective in blocking both tumor invasion and metastasis.