The soybean aphid, Aphis glycines Matsumura, is a serious pest of soybean [Glycine max (L.) Merr.] in the USA and Canada, and a sporadic pest of soybean in Asia. Infestations by soybean aphid cause economic loss to soybean through reductions in seed yield and oil concentration. Aphid-resistant soybean lines are needed to supplant insecticides for managing soybean aphid, and resistant lines may be developed from both domesticated and wild soybean lines. Free-choice assays of 42 lines of wild soybean (Glycine soja Siebold and Zucc.) in this study identified line 99PI522233 as resistant to soybean-aphid biotype 1. That line was advanced for follow-up assays with wild soybean lines PI 469399 B, PI 507825, PI 507840 and PI 507843, which had previously been screened as aphid resistant. Line 99PI522233 had significantly fewer soybean aphids than other lines except the resistant check in the second and third weeks of a no-choice assay, but the four other putatively resistant lines did not show resistance in the no-choice assay. Thus, line PI99522233 may be advanced for genetic characterization of its resistance, and it should be tested for resistance against virulent soybean aphid biotypes.