Genome segment S9's of rice black-streaked dwarf virus (RBSDV) of three Chinese isolates were amplified by RT-PCR and sequenced, and were found to be consisted of 1 900 nt (RBSDV-Zj S9 EMBL accession number AJ297430),1 898 nt (RBSDV-Heb S9 EMBL accession number AJ297429) and 1 900 nt (RBSDV-Hub S9 EMBL accession number AJ291706), respectively. Genome segment S9's of three Chinese Isolates shared 98.5%--98.8% sequence homology and all contained two open reading frames (ORF), which encoded two polypeptides with moleclular weights of 40 kD and 24 kD, respectively. Amino acid sequence comparison of the polypeptides encoded by the second ORF of the corresponding genomic segment of five isolates, including three Chinese isolates, Japanese isolate, and Italian MRDV (maize rough dwarf virus), were highly conserved.