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Objective: The objective of this study was to evaluate the action of soy isoflavones (ISO) and 17β-estradiol on collagen I (CollI) and sulfated glycosaminoglycans (GAGs) in the bone matrix of diabetic rats. Methods: Sixty adult female rats ( Rattus norvegicus albinus ) underwent ovariectomy, and then were randomized into six groups of 10 animals each: GI, sham control ovariectomized animals; GII, sham control diabetic (DM) ovariectomized animals; GIII, control ovariectomized animals receiving propylene glycol vehicle; GIV, control ovariectomized DM animals receiving propylene glycol vehicle; GV, ovariectomized DM animals treated with ISO (150 mg/kg by gavage); and GVI, ovariectomized DM animals treated with estrogen (17β-estradiol, 10 mg/kg, subcutaneously). 17β-Estradiol was used as a positive control when compared with ISO. To obtain significant depletion of the estrogen levels and subsequent bone loss, a postsurgical period of 90 days was observed. Treatments occurred during 30 consecutive days. After euthanasia, shafts of the animals' femurs were immersed in liquid nitrogen for molecular biology analysis, and the distal femurs were removed and processed for paraffin embedding. Results: ISO (GV) and 17β-estradiol (GVI) improved bone formation, increasing GAGs and CollI formation when compared to the control group (GIV) ( p  < 0.05). Conclusions: ISO and 17β-estradiol contribute to the decrease of bone loss in diabetic rats.