In order to develop a nested PCR method for the detection of Mycoplasma hyopneumoniae(Mhp), two pairs of specific primers for nested PCR were designed referring to the conserved region gene fragment of Mhp P36 gene deposited in GenBank, and the reaction conditions were optimized.Mhp of 168 isolates, Mycoplasma Galliscepticum, Mycoplasma hyorhinitis,Streptococcus suis, Actinobacillus pleuropneumoniae, Haemophilus parasuis, Porcine circovirus type 2, and Pseudorabies virus were detected using this method.The results showed that the method could amplify the 793 bp and the 448 bp target gene of Mhp specifically by using the two pairs of specific primers, resp., and had no cross reaction with any of others.The sensitivity of the nested PCR was 10 copies/μL, which was more sensitive of 100 times than that of conventional PCR kit. 50 samples of culture medium DNA containing Mhp were tested by using the developed nested PCR, conventional PCR and Mycoplasma isolation and culture methods, the pos. detection rates of 88%, 82% and 88%, resp.The total coincidence rate of nested PCR and conventional PCR was 94%, and that of Mycoplasma isolation and culture method was 100%.The nested PCR method developed in this study can be used for the epidemiol. investigation of Mhp.