Increasing resource use is the primary motivator for the development of technology industries, which is leading to severe consequences, such as the release and disposal of radioactive waste containing radionuclides in the environment. Cesium (137Cs) is one of the most hazardous radionuclides in the environment. In particular, the steel manufacturing process produces hazardous waste in the form of electric arc furnace dust contaminated with 137Cs. In this study, the tolerances of five legume species to different activity concentrations of 137Cs in both seed germination and initial seedling growth were compared. To determine 137Cs tolerance, several parameters related to the growth and development of legumes were measured. Among the five legumes studied, Crotalaria juncea L. was the most 137Cs tolerant at 50,000 Bq·L−1. Sesbania javanica Miq. and Vigna mungo L. Hepper were moderately tolerant to 30,000 Bq·L−1 137Cs. After 10 days, the stress tolerance indices in all legume species decreased by more than 50% at activity concentrations greater than or equal to 20,000 Bq·L−1 137Cs. This approach allows the selection of desirable traits, making more-effective application possible in the phytoremediation of 137Cs through stress tolerance. In conclusion, legumes are promising candidates for the phytoremediation of environmental pollutants.