According to the nucleotide sequence of the S1 gene of MDRV registered in GenBank, a set of primers C1 ,HPll and HP12 were designed to amplify a specific 300 bp fragment by semi-nested RTPCR. The specific product could only be amplified from MDRV, but not from ARV,GPV,MPV,CEF and MDEF cell cultures by this method. The detectable dsRNA amount by this method was 1 fg and which had high specificity and repeatability. Pathological tissues of artificial infection and suspicious clinical samples were diagnosed by virus isolation and semi-nested RT-PCR. The coincidence rate of the two methods was 100%. So this semi-nested RT-PCR could be used for rapid detection of the muscovy duck reovirus disease.