In this study, we investigated the therapeutic effects of black corn polysaccharide (BPS) on diabetic osteoporosis (DOP) in rats and sought to elucidate the underlying mechanisms. Methods: A DOP rat model was established by feeding rats a high-fat diet combined with streptozotocin (STZ) injection. The rats were randomly assigned to one of the following five groups: Model, low-dose BPS, high-dose BPS, metformin, and blank control groups. Metabolic parameters, including fasting blood glucose (FBG), food and water intake, and body weight were monitored, and we collected serum, femur, and tibia samples. In addition, using ELISA, we determined the serum levels of glycosylated hemoglobin (GHb), 1,25-(OH)₂D₃, parathyroid hormone (PTH), N-terminal propeptide of type I procollagen (PINP), tartrate-resistant acid phosphatase 5b (TRACP-5b), C-terminal telopeptide of type I collagen (CTX-I), osteoprotegerin (OPG), and receptor activator of nuclear factor-κB ligand (RANKL). Furthermore, morphometric measurements of cortical and cancellous bones were performed based on observations of hematoxylin and eosin-stained tissues, whereas femoral biomechanical properties were assessed using a three-point bending test, and the protein expression of OPG and RANKL in tibia was determined immunohistochemically. Results: BPS treatment was found to promote significant reductions in the serum levels of GHb (P<0.01) and FBG (P<0.01), along with reductions in the bone resorption markers TRACP-5b (P<0.01) and CTX-I (P<0.01), and increases in the levels of PTH (P<0.05), 1,25-(OH)₂D₃ (P<0.01), PINP, OPG and OPG/RANKL ratio (P<0.05 or P<0.01). BPS also contributed to an improvement in tibial bone microstructure by promoting increases in the percentage trabecular area (%Tb.Ar), trabecular number (Tb.N), cortical bone area (Ct.Ar), and bone marrow cavity area percentage (%Ma.Ar), whilst reducing trabecular separation (Tb.Sp). Moreover, BPS enhanced femoral biomechanical properties, including maximum load (P<0.01), maximum energy absorption (P<0.01), structural toughness (P<0.01), and elastic modulus (P<0.01). In addition, BPS was found to promote upregulated OPG and downregulated RANKL expression in bone tissue. Conclusion: In DOP rats, the administration of BPS effectively improves glycemic control, ameliorates bone metabolic disorders, and enhances bone strength, plausibly via regulation of the OPG/RANK/RANKL signaling pathway. These findings will provide a theoretical basis for developing BPS as a potential therapeutic agent for the treatment of diabetic osteoporosis.