Satellite RNAs (satRNAs) are molecular parasites that interfere with the pathogenesis of the helper viruses. In this study, the relative accumulation of cucumber mosaic virus (CMV)-Fny genomic RNAs with or without satRNAs were quantitatively analyzed by real-time RT-PCR. The results showed that satRs apparently attenuated the symptoms of CMV-Fny on Nicotiana tabacum by depressing the accumulation of CMV-Fny genomic RNAs, tested as open reading frames. The accumulation of CMV-Fny 1a, 2a, 2b, 3a, and CP genes was much higher than that of CMV-Fny with satRs added (CMV-Fsat), at different inoculation times. CMV-Fnyδ2b, in which the complete 2b gene and 41 amino acids at the C-terminal of the 2a gene were deleted, caused only a slight mosaic effect on N. tabacum seedlings, similar to that of CMV-Fsat, but the addition of satRs to CMV-Fnyδ2b showed further decrease in the accumulation of CMV-Fnyδ2b genomic RNAs. Our results indicated that the attenuation of CMV, by adding satRs or deleting the 2b gene, was due to the low accumulation of CMV genomic RNAs, and that satRNA-mediated reduction of CMV genomic RNAs accumulation in N. tabacum was possibly related to the 2b gene.