An one-step Multiplex RT-PCR assay was developed using two pairs of primers(PH1/PH2 and PT1/PT2) designed according to the conservative sequences of porcine circovirus type 2(PCV2) ORF2 and porcine respiratory and reproductive syndrome virus(PRRSV) ORF5 respectively.PCV2 DNA and PRRSV RNA was extracted from the mixed sample of PCV2 and PRRSV and used as PCR template.Two specific PCR fragments of PCV2 560 bp and PRRSV 398 bp were amplified.No PCR products were detected from other four porcine pathogenic viruses.The assay has a sensitivity of detecting 10 ng of PCV2 DNA and 5 ng PRRSV RNA.