ABSTRACT Quasispecies represent a general evolutionary model for most RNA viruses and other viruses with high mutation rates. However, quasispecies have not been previously reported in the grass carp reovirus (GCRV), which has caused severe hemorrhagic disease in grass carp in China for several decades. This study revealed the presence of multiple co‐existing mutant sequences within individual viral strains, indicative of a quasispecies distribution in GCRV strains through Sanger sequencing of viral genomic segments. Different viral strains exhibited varying degrees of quasispecies diversity and heterogeneity, potentially establishing a basis for viral evolution in response to environmental changes and host adaptation. This study provides novel insights into the genetic variation and evolution of GCRV, which will not only enhance the understanding of GCRV transmission and prevalence but also facilitate the development of vaccines against grass carp hemorrhagic disease.