The c-erbB-2 proto-oncogene encodes a 185kDa protein p185, which belongs to epidermal growth factorreceptor family. Amplification of this gene has been shown to correlate with poor clinical prognosis forcertain cancer patients. The monoclonal antibody A21 which directed against p185 specifically inhibitsproliferation of tumor cells overexpressing p185, hence allows it to be a candidate for targeted therapy. Inorder to overcome several drawbacks of murine MAb, we cloned its VH and VL genes and constructed thesingle-chain Fv (scFv) through a peptide linker. The recombinant scFvA21 was expressed in Escherichiacoli and purified by the affinity column. Subsequently it was characterized by ELISA, Western blot, cellimmunohistochemistry and FACS. All these assays showed the binding activity to extracellular domain(ECD) of p185. Based on those properties of scFvA21, we further constructed the scFv-Fc fusion moleculewith a homodimer form and the recombinant product was expressed in mammalian cells. In a series ofsubsequent analysis this fusion protein showed identical antigen binding site and activity with the parentantibody. These anti-p185 engineered antibodies have promised to be further modified as a tumor targetingdrugs, with a view of application in the diagnosis and treatment of human breast cancer.