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The experiment was conducted to evaluate the effect of dietary supplementation with isoflavones on exterior development and tibia bone quality of laying hens. Eighty laying hens, 20 weeks old, were divided into 5 groups, 20 in each and fed with different amount of 300, 600, 1200 and 1800 mg.kg-1 supplemented isoflavones (SI) in the feed. Dietary isoflavones supplemented in different concentrations to the ISA Brown laying hens diet caused increase of the body weight (P < 0.05). The heaviest body weight was noticed in the group fed with supplementation of 1800 mg.kg-1 SI (2142.5 ± 190.5 g). In addition, shank length as an important measurement of skeletal development was significantly longest in the group fed with supplementation of 1800 mg.kg-1 SI (29.50 ± 1.73 cm). There were no differences in other exterior parameters among the experimental groups (P > 0.05). High SI treatment (1800 mg.kg-1 feed) had a beneficial effect (P < 0.05) on bone quality of aged laying hens (weight, volume, ash/tibia and calcium), but do not affect on the tibial phosphorus (P > 0.05). Results of the present study indicates that isoflavones are effective supplements to improve the body weight and calcium bone content during the late laying period, even though their supplementation was high.