Sendai virus (SeV) is one of the most prevalent viral pathogens infecting laboratory mice and rats. To date, mature SeV virions have been used as antigens for serological diagnosis. To develop antigens that are more specific and easier to prepare for diagnosis, we examined the antigenic sites in the nucleocapsid protein (NP) of SeV with antisera from experimentally SeV-infected mice and a peptide array membrane containing overlapping 10-mer peptides covering the entire NP. We found antigenic linear sequences in two regions, amino acids 120-160 and 420-500, of the SeV-NP. From these antigenic sequences, we applied two synthesized peptides, IVKTRDMEYERTTEWL and FVTLHGAERLEEETNDE, which correspond to positions 119-134 and 458-474 of the SeV-NP, respectively, as antigens in an enzyme-linked immunosorbent assay (ELISA). Evaluation of the ELISAs using these peptides revealed that they were specific to anti-SeV antisera. Furthermore, the ELISAs using these peptides were able to distinguish between SeV-positive and SeV-negative mouse sera to the same extent as a commercial ELISA kit. These results indicate that these peptides are useful for the serological diagnosis of SeV infection.