Technical Abstract: Ranchers need to provide alternative livestock feeds when herbaceous forages become limiting in summer. We determined foliar yield components and nutritive value (in vitro digestibility [IVDMD], total nonstructural carbohydrate [TNC], N, robinin, and mimosine) of transplanted Robinia pseudoacacia (black locust) and Albizia julibrissin (mimosa) trees pollarded at 50 cm in Arkansas, USA. Black locust exceeded mimosa for every yield component (foliage mass/tree, leaves/shoot, shoots/tree, shoot mass/tree, basal area, and biomass/tree) except mass leaf. Projected foliar yields were 1900 and 1600 kg foliage/ha for black locust and mimosa, respectively, assuming a population of 12300 trees/ha. Mimosa foliage had greater IVDMD, TNC, and N digestibility than black locust. Mimosa foliage exceeded the nutritional N requirements of growing cattle (Bos taurus) and goats (Capra hircus), but protein supplementation would be needed for growing goats grazing black locust foliage. Concentrations of robin in and mimosine were below detectable limits in black locust and mimosa, respectively. The extract of black locust bark, but not foliage, was toxic to bioassayed monkey (Cercopithecus aethiops) cells. Either black locust or mimosa could provide moderate quantities of high quality, rotationally grazed forage for cattle or goats during summer months when herbaceous forage may in short supply.