Abstract: An attenuated vaccine strain of Muscovy Duck Reovirus(MDRV),which was suitable for propagating in chicken embryo fibroblast(CEF),was obtained by serial passage alternately between Muscovy duck embryo fibroblast(MDEF)and CEF.The attenuated strain was proven to be not pathogenic to one-day-old Muscovy ducklings and the TCID50 to CEF stable between 10-5.0-10-5.5;no reversion of virulence for five passages continuously after introduction to one-day-old Muscovy ducklings;and negative on the exogenous virus test.The protection rate of the attenuated strain was greater than 88%,when the ducks were challenged with a virulent strain of MDRV 7 days after vaccination.The results indicated that attenuated vaccine strain of MDRV could be used as a live vaccine against MDRV,as it was free from exogenous virus contamination,and exhibited acceptable genetic stability,excellent safety and effective immunogenicity.