The over|expression of collagenase IV in tumor tissues was found to be closely related to tumor metastasis. Collagenase IV has been therefore considered as one of the novel indicative molecules for tumor diagnosis and treatment. Based on phage display antibody library technique, a single|chain Fv specific for collagenase IV was successfully cloned. This antibody, referred to as hCo4, was mainly composed of variable regions from heavy and light chains, with its molecular weight of 27 ku. The engineered antibody bound to collagenase IV specifically. The affinity of hCo4 was found to be the same as that of a single|chain antibody constructed from a monoclonal antibody to collagenase IV. Since hCo4 is the smallest among all the antibodies specific for collagenase IV and it is of human origin, it has a potential to be applied for tumor immunotherapy and for the study of the relationship between collagenase IV and tumor metastasis. The over | expression of collagenase IV in tumor tissues was found to be closely related to tumor metastasis. Collagenase IV has been therefore considered as one of the novel indicative molecules for tumor diagnosis and treatment. Based on phage display antibody library technique, a This antibody, referred to as hCo4, was mainly composed of variable regions from heavy and light chains, with its molecular weight of 27 ku. The engineered antibody bound to collagenase IV specifically . The affinity of hCo4 was found to be the same as that that a single | chain antibody constructed from a monoclonal antibody to collagenase IV. Since hCo4 is the smallest among all the antibodies specific for collagenase IV and it is of human origin, it has a potential to be applied for tumor immunotherapy and for the study of the relationship between collagenase IV and tumor metastasis.