Abstract: Seven strains of cytoplasmic polyhedrosis viruses of Dendrolimus spp. were isolated and pured by sucrose gradient ultracentrifugation and examined under scanning electronic microscope.A comparison study on their RNA genome segments had been made.There was only one sedimental band formed after ultracentrifugation in 5 of them-JDS-CPV,JGDP-CPV,JYDPW-CPV,JADP——CPV,and CYDPW-CPV.But there were two sedimental bands formed in both JHDS-CPV and CGDP-CPV.The shape of the cytoplasmic polyhedral bodies from the sedimental bands of the 5 CPVs and the lower sedimental bands of JHDS-CPV and CGDP-CPV appeared to be typical hexagonal.The RNA genomes extracted from the CPBs in vertical slab 3% PAGE or 1% agarosegel electrophoresis similar to Bombyx type.But there were differences between JDS-CPV in 3% disc PAGE and its replicates.The shape of the CPBs from the upper sedimental band of JHDS-CPV and CGDP-CPV appeared to be pyramidal.The RNA genome of JHDS-CPV and CGDP-CPV had 13 segments in 1% agarose gel electrophoreses and belonged to neither Bombyx type nor anyone of 12 genome types suggested by C.C.and C.F.Rivers.For this,both JHDS-CPV and CGDP-CPV might be a mixture of two strains of CPV,which has not been reported before.