The soybean aphid, Aphis glycines Matsumura 1917, is well known as a soybean pest in the world. Recently, it has been introduced to North America causing serious damage in U.S. As a cooperative research with USDA-ARS, we have investigated A. glycines in soybean fields, and also examined the colonies on the overwintering host Rhamnus davurica in order to find its natural enemies. It was generally reported that A. glycines has host alternation between the soybean, Glycine max (summer host) and the Dahurian buckthorn, Rhamnus davurica (winter host) in East Asia. However, it was very difficult to identify the soybean aphid, A. glycines, from R. davurica due to the co-existance of at least three Aphis species and the seasonal polymorphisms of each species (e.g, gynopara, ovipara, and male). For species identification, we tested 3 molecular markers, mitochondrial COI, COII, and nuclear EF1α, for 14 collected samples (7 samples from G. max and 7 samples from R. davurica). As a result, we found two different species, A. gossypii and other Aphis sp., are mixed together with A. glycines on R. davurica. We report the biology of A. glycines in Korea, and present species identification using molecular phylogenetic approach.