A novel Bombyx mori cypovirus 1 isolated from infected silkworm larvae and tentatively assigned as Bombyx mori cypovirus 1 isolate Suzhou (BmCPV-SZ). The complete nucleotide sequences of genomic segments S1-S10 from BmCPV-SZ were determined. All segments possessed a single open reading frame; however, bioinformatic evidence suggested a short overlapping coding sequence in S1. Each BmCPV-SZ segment possessed the conserved terminal sequences AGUAA and GUUAGCC at the 5' and 3' ends, respectively. The conserved A/G at the -3 position in relation to the AUG codon could be found in the BmCPV-SZ genome, and it was postulated that this conserved A/G may be the most important nucleotide for efficient translation initiation in cypoviruses (CPVs). Examination of the putative amino acid sequences encoded by BmCPV-SZ revealed some characteristic motifs. Homology searches showed that viral structural proteins VP1, VP3, and VP4 had localized homologies with proteins of Rice ragged stunt virus , a member of the genus Oryzavirus within the family Reoviridae. A phylogenetic tree based on RNA-dependent RNA polymerase sequences demonstrated that CPV is more closely related to Rice ragged stunt virus and Aedes pseudoscutellaris reovirus than to other members of Reoviridae, suggesting that they may have originated from common ancestors.