Morphology, chromosome and transmission of potato virus Y(PVY) of the green peach aphid populations collected from tobacco fields were examined. Based on the morphological characteristics, especially values of linear discriminant functions and length of ultimate rostral segment, 8 green peach aphid clones with different color morphs could be divided into two groups, namely Myzus persicae and M. nicotianae, according to the proposal by Blackman in 1987. The red (RED)-, Brown (BRN)- and green-colored (GR1, GR2) aphid clones belonged to the M. nicotianae type, while the pale green (PG1, PG2, PG3) and dark brown (DBR) clones to the M. persicae type. The karyotype of the pale green-colored clone (PG1, M. persicae type) appeared normal and was 2n=12 with no indication of chromosomal translocation. On the contrary, in the green-colored aphid clone (GR1, M. nicotianae type), translocation and dissociation of autosome 3 were often found, having karyotype of 2n=13. Both of the above aphid clones transmitted PVY-VN to tabacco plants (cv. Burley 21), but the GR1 clone had higher transmissibility than the PG1 clone. Key words : green peach aphid, potato virus Y, morphology, karyotype transmission