In southern Korea, the two aphid species, Myzus Pessicae(Sulzer) and Lipaphis Pseudobrassicae (Davis), had been known to have sexual phase to produce hibernating eggs on their alternate hosts. However, we have fequently found that they were still alive in the parthenogenetic form even in below freezing conditions in winter. This study had been focused on verifying the possibility of overwintering of the two important aphid species in the parthenogenetic morph, by comparing the population density changes within greenhouse and open field condition. In green- house condition, though not heated, both species successfully continued reproducing in a parthenogenetic form. In open field, L. pseudobrassicae successfully survived and reproduced on chinese cabbage and spinach even below freezing temperatures. M. persicae were also able to survive in the winter but not as much capability of reproduction as L. preudobrassicae. This study provided the evidence that the aphid infestations in greenhouse can be mostly from overwintering populations in the parthenogenetic morph in southern greenhouse area of Korea.