The soybean aphid [Aphis glycines Matsumura] is an important pest of soybean [Glycine max (L.) Merr.] in North America. Kansas soybean line, K1621, possesses moderate resistance to soybean aphid. The objective of this study was to identify the inheritance of the resistance in K1621. One-hundred fifty-two F2:3 families from the cross between K1621 and susceptible genotype KS4202 were evaluated for soybean aphid resistance. Phenotyping of the population was conducted in greenhouse using a randomized complete block design with three replications. Each family contained up to 22 F3 plants. Aphid number on each plant was counted seven days following infestation. Significant variance was observed for aphid number among the F2:3 lines (p<0.05). The mean aphid number in each F2:3 lines continuously ranged from 6.2±4.9 to 42.7±5.3. The number of aphid on parents K1621 and KS4202 was 11.27±4.09 and 28.81±3.89, respectively. To identify genes associated with soybean aphid resistance, two parents were tested with 527 simple sequence repeat markers for polymorphism and mapping of possible QTL's is underway using polymorphic SSR markers.