A polypeptide for inhibiting, treating or diagnosing metastasis and an use thereof are disclosed, wherein the polypeptide is a polypeptide, a derivative polypeptide, or a mutated polypeptide of a fibronectin-binding domain of dipeptidyl peptidase IV. In addition, a pharmaceutical composition treating or diagnosing metastasis is also disclosed, which comprises the aforementioned polypeptide, and a pharmaceutically acceptable carrier.
