Plant Systems Engineering Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon 305-333, Korea(Received on October 5, 2010; Accepted on October 27, 2010)In 2006 fall, a preliminary survey of viruses in two important medicinal plants, Cynanchum wilfordii and C.auriculatum, was conducted on the experimental fields at the Agricultural Research and Extension Services ofChungbuk province in Korea. On each experimental fields, percentage of virus infection was ranged from 20to 80%, and especially an average of disease incidence propagated by roots was twice higher than that byseeds. The various symptoms were observed in Cynanchum spp. plants, such as mosaic, mottle, necrosis,yellowing, chlorotic spot and malformation etc. In electron microscopic examination of crude sap extracts,filamentous rod particles with 390-730 nm were observed in most samples. The virus particles were purifiedfrom the leaves of C. wilfordii with typical mosaic symptom, and the viral RNA was extracted from thissample containing 430-845 nm long filamentous rod. To identify the viruses, reverse transcription followed byPCR with random primers was carried out. The putative sequences of P3 and coat protein of potyvirus wereobtained. From a BLAST of the two sequences, they showed 26-38% and 62-72% identities to potyviruses,respectively. In SDS-PAGE analysis, the subunit of coat protein was approximately 30.3 kDa, close to the coatprotein of potyvirus. In bioassay with 21 species in 7 families, Chenopodium quinoa showed local lesion oninoculated leave and chlorotic spot on upper leave, but the others were not infected. RT-PCR detection usingspecific primer of C. wilfordii and C. auriculatum samples, all of 24 samples with virus symptom was positive,and five out of seven samples without virus symptom were also positive. On the basis of these data, the viruscould be considered as a new member of potyvirus. We suggested that the name of the virus was Keunjorongmosaic virus (KjMV) after the common Korean name of C. wilfordii.Keywords : Cynanchum wilfordii, Cynanchum auriculatum, Keunjorong mosaic virus, Medicinal plants,Virus disease