Abstract: On the basis of the 16S ribosomal DNA（rDNA） sequences, the DNA extract-ed from Bacillus piliformis，Escherichia coli，HemoLytic streptococcus,Pasteuralla pneumotroopica were amplified by PCR using 2 pairs of PCR specific primers. With out-er-primers，a DNA fragment of the expected size （625bp） was amplified from Bacillus piliformis and E.coli, but no band was observed in Hemolytic streptococcus and Pasteu-ralla pyieumotroopica. Whereas a 196bp fragment was obtained only from Bacillus pili-formis with inner-primers. Thirty liver samples from immunosuppressive rats were de-tected for Bacillus piliformis by using nested PCR, the positive rate is 30% （9/30），but no serum sample is positive monitored by IFA. In conclusion, the 16S rDNA-based PCR established is sensitive and specific in detection of Bacillus piliformis in infected ani-mals.