Oxidative stress (OS) promotes bone loss after menopause, and there is evidence that dietary antioxidants may reduce the level of OS in vivo. This study examined dose-dependent effects of blackberries (BBs) containing mainly cyanidin 3-O-β-d-glucoside (C3G) in preventing bone loss in an ovariectomized (Ovx) rat model. Nine-month-old female (N=38) Sprague-Dawley rats were scanned using dual-energy X-ray absorptiometry for baseline whole body, bone mineral content (BMC), and bone mineral density (BMD). One group was sham operated (Sham) and three groups were ovariectomized (Ovx). The groups and corresponding diets were Sham+control diet (n=12), Ovx+control diet (n=12), Ovx+5% BB (n=7), and Ovx+10% BB (n=7). Control diet was AIN-93M rodent diet, and the Ovx+5% BB and Ovx+10% BB were a diet modified to contain powdered, freeze-dried BB at levels of 5% and 10% (w/w). Following 100 days of treatment, whole body BMC and BMD were reassessed and bone specimens, blood, and 24-h urine samples were collected for analyses. Findings indicate that ovariectomy (Ovx) compromised whole body BMC and trabecular microarchitecture of the proximal tibia and fourth lumbar vertebra. C3G-rich BB at the level of 5% modestly protected BMDs, loss of the tibia, lumbar vertebra, and femur by 2.4%, 2.7%, and 4.3% (P<.0013; .0437; .0004), respectively. BB 5% treatment significantly prevented loss of tibial trabecular bone volume and trabecular number by 37% and 21%, respectively (P<.05), and also significantly prevented tibial trabecular separation by 22%. We conclude that C3G-rich BB treatment at the level of 5% (w/w) but not at 10% (w/w) may modestly reduce Ovx-induced bone loss evident by improved tibial, vertebral, and femoral BMD values, and tibial bone microstructural parameters. Bone protective effects may be as a result of the synergistic effects of phenolic compounds; however, further work is required to determine BBs' specific mechanisms of action.