Seven overlapping truncated forms of the C subunit of porcine aminopeptidase N (pAPN-C) were expressed in Escherichia coli. By western blotting and ELISA test, all recombinant proteins were recognized by the antibody against native porcine aminopeptidase N. Recombinant proteins, rpAPN-C2 (aa 623-722) and rpAPN-C3 (aa 673-772), had the highest binding activity with swine transmissible gastroenteritis virus among the truncated pAPN-C recombinant proteins. The overlapping region (aa 673-722) between rpAPN-C2 and rpAPN-C3 is indicated to play a key role in viral binding.