Disclosed is a method for determining metastatic potential of tumors, a method and a composition for treating/suppressing metastasis of cancers, as well as a method for obtaining a metastasis suppressor. A particular aspect of the invention relates to a method and a composition of evaluating expression levels of connective tissue growth factor (CTGF, also known as CCN2) to determine the status of tumor invasion. Another aspect of the invention relates to a method and a composition comprising a tumor suppressor, which maintains or increases an expression level of CTGF to suppress the invasion ability of tumor cells effectively. In another aspect of the invention relates to methods for obtaining a metastasis suppressor by evaluating the expression levels of CTGF after contacting suppressor candidates with a tumor cell line system.