The nasal swabs and serum samples from 260 pigs were collected for M. hyopneumoniae SIgA and IgG detection with the SIgA-ELISA and a commercial M. hyopneumoniae ELISA kit (IgG-ELISA), respectively. The results of SIgAELISA and IgG-ELISA were assessed according to the result of nested-PCR and immunity background of pigs.