The complete nucleotide sequence of an isolate of Ribgrass mosaic virus (RMV-Sh) from Brassica chinensis (Qingcai) in Shanghai, China was determined. The genome consisted of 6301 nucleotides and its genomic organization was similar to those of other crucifer-tobamoviruses. Comparisons of the nucleotide and predicted amino acid sequences and phylogenetic analyses showed that RMV-Sh had very high homology (> 95% identical nucleotides and 97.7-99.6% identical amino acids) to a sequence of Youcai mosaic virus (YMV = Chinese rape mosaic or Oilseed rape mosaic virus), despite differences in host range or symptoms and this strongly suggests that these isolates should be regarded as belonging to the same species. Only coat protein sequences have been reported for other RMV isolates but it seems likely that the distinction between RMV and YoMV will be difficult to maintain.