Abstract: Based on the ORF7 gene sequence of the porcine reproductive and respiratory syndrome virus(PRRSV),a pair of primers were designed and synthesized.By means of the template of RNA of PRRSV,the RT-PCR technique for detecting PRRSV was established.The 443 bp specific fragments were obtained subsequently from our laboratory’s virocyte culture.Negative test results were found on the Porcine Circovirus Type 2,Pseudorabies Virus,Classical Swine Fever Virus,and Marc-145 cells.The amplified sequence of PCR product was 92%-98% in agreement with those published data on PRRSV strains.The sensitivity of RT-PCR reached 2.39TCID50.In 2004-2005,23.4% of the 81 clinical specimens tested to be positive.The results showed that the newly developed RT-PCR method had high specificity and sensitivity,and that it could be applied for PRRSV diagnosis and epidemiological investigation.