We conducted a randomized controlled trial to examine whether supplementation with soy peptide enhanced the effects of resistance training for community-dwelling frail elderly. The subjects comprised 33 elderly persons who had reported one or more fall experiences in the previous year (designated as “fallers”), and 50 elderly persons who had two or more geriatric syndromes among fall experience, urinary incontinence, disability in one or more items of five instrumental activities of daily living, and a low frequency of going outdoors. The subjects within each subgroup were randomly allocated into an exercise group and exercise plus nutritional supplementation group. Both groups participated in 1-hour supervised resistance training classes twice a week for 12 weeks. The nutritional supplementation group was given a soy-peptide beverage equivalent to an intake of 32 g of soy protein per week during this period. After the 12-week intervention period, the exercise plus nutritional supplementation group within the fallers showed a greater improvement in knee-extension power and usual walking speed, and greater reduction of white blood cell count than the exercise group. However, no significant additive effect of supplementation was apparent in the multiple-geriatric syndrome subgroup. Supplementation of soy peptide may enhance the effect of resistance training in a certain subset of the frail elderly.