The nucleocapsid (N) protein of rinderpest virus (RPV) is highly conserved, immunogenic, and abundantly expressed during infection. Six antigenic sites (sites A, B, C, D, E and F), defined previously by a competitive binding assay using corresponding monoclonal antibodies (Mabs), have been further localized by immunoassays using deleted N mutants. Five different forms of RPV N protein, containing residues aa 1-79, aa 1-149, aa 1-421, aa 414-525 and aa 1-525, were expressed as glutathione S transferase (GST) fusion proteins (designated as GST-N1-79, GST-N1-149, GST-N1-421, GST-N414-525, and GST-N1-525, respectively) in E.coli BL21 cells. In ELISA using deleted N mutants, Mabs recognizing sites A, B, C, D and E reacted with 3 GST fusion proteins (GST-N1-149, GST-N1-421 and GST-N1-525), indicating that they are located at aa 80-149. Mab recognizing site F reacted with 4 GST fusion proteins (GST-N1-79, GST-N1-149, GST-N1-421 and GST-N1-525), indicating that site F is located at aa 1-79. Identification of the amino-terminal antigenic sites of the N protein would provide antigen basis for developing sensitive and specific diagnostic reagents for RPV, although it remains to be further investigated antigenic sites at the carboxyl-terminus.