Both grapevine fanieaf virus and potato virus Y biotin-labelled ds-cDNA probes were synthesized by polymerase chain reaction using recombinant coat protein gene as template. The optimum concentration of ds-cDNA probes were 1:100 in dot blot hybridization. The sensitivity of detection for GFV-RNA was 10 pg,partially purified GFV was 25pg,the maximum dilution of GFV-infected Chenopodium amaranticolor leaves extract was 1:10000; The sensitivity of detection for PVY-RNA was 30pg, partially purified PVY was 500pg,the maximum dilution of PVY infected Nicotiana tabacum leaves extract was 1:8000. There were no any hybridization signales in the negative control.