OBJECTIVE In order to reduce the immunogenicity of the murine antifibrin monoclonal antibody (MAb) SZ-63 to human beings. METHODS First of all, the cDNA sequences encoding the constant regions of the murine kappa light chain and gamma 1 heavy chain in the SZ-63 MAb were substituted with the corresponding human genomic sequences. Then the constructed MAb was cloned separately into two selectable expression vectors, and the latter were transfected into mouse myeloma cells (SP2/0) one by one. RESULTS ELISA, Western blot and competition experiment results showed that there was 0.8 approximately 1.0 mg/L of chimeric 63 IgG in the conditioned medium of selected cell lines, and the expressed IgG had higher antifibrin D-Dimer capability than that of the original MAb. CONCLUSIONS The expressed chimeric antibody can be used as a targeting agent for thrombus imaging and treatment.