| In order to study the virulence and biological characteristics of different isolates of grass carp reovirus (GCRV) type II, we researched two new isolates of genotype II GCRV, ZH1808 and CQ1807, which were isolated from diseased and healthy grass carp respectively. The characteristics of cell culture, pathogenicity, genomic segment, gene sequence and phylogenetic differences of the two strains were compared and analyzed. The result showed that mortality rate of ZH1808 to grass carp and gobiocypris rarus were 80%, 100%, and those of CQ1807 were 10%，0% respectively. The data of mortality rate showed that ZH1808 is a virulent strain, and CQ1807 is an avirulent strain. Cell infection experiment showed the two isolates could proliferate in GSB, GRE and GRF cells, but did not cause cytopathic effect (CPE), and viral multiplication of ZH1808 strains was more than 1,000 times that of CQ1807 strains. The banding patterns of two isolates in SDS-PAGE were partially identical, but there were some differences between the segments of S7, S8, S9, S10 and S11. The sequence homology of the S7 and S11 genes between two viruses are 98% and 99%, respectively. Phylogenetic analysis indicated that isolate ZH1808 and CQ1807 are belong to the same branch, its means that they are very closely related.All results above indicate that two strains of GCRV type II isolated from diseased and healthy grass carp have more common characteristics, but their replication ability and pathogenicity are also different.