Abstract: Muscovy duck reovirus(MDRV) and Novel duck reovirus(NDRV),which belong to Orthoreovirus,are important pathogens of waterfowl.This study was conducted to compare the biological characteristics of MDRV and NDRV.Several methods were undertaken such as ultrathin sections observation,cross virus-neutralization test,the pathogenicity to avian embryos and cell lines,comparison of genome segment profiles and the characteristics analysis of S3 gene.The results of ultrathin sections observation showed that MDRV and NDRV viral particles were spherical and the diameter was both about 70 nm.MDRV scattered in MDEF cytoplasm,whereas NDRV particles arranged in crystal lattice.Relatedness(R) values showed that the antigen of the two viruses were generally different.MDRV′s CPE feature was cell rounding,while which of NDRV was cell fusion.NDRV induced the death of 9-day-old chicken embryos,whereas MDRV did not.The migration profiles of NDRV and MDRV genome segments were different.The S3 genes of the two viruses were at different branches of molecular phylogenetic tree.In conclusion,the biological characteristics of MDRV and NDRV were obviously different.