As the global population ages, the prevalence of osteosarcopenia—a combined condition of osteoporosis and sarcopenia—poses significant health challenges, leading to increased frailty, falls, and chronic disability in the elderly, especially for postmenopausal women. Nutritional interventions targeting age-associated physiological decline present promising strategies for managing these conditions. In this study, the preventive effects of total Lycium barbarum polysaccharide (LBP), acidic LBP (ALBP), and neutral LBP (NLBP) on osteosarcopenia were systematically evaluated using an ovariectomized (OVX) mouse model. Our findings showed that ALBP significantly improved physical performance, bone strength, and bone density, while enhancing muscle mass and fiber size, thereby effectively alleviating osteosarcopenia. Mechanistic investigations revealed that ALBP elevated the expression levels of osteoblast-associated genes such as Alp, Col1a1, Runx2, Opn, upregulated key myogenic genes, including Myh2, Myh4, Myh7, while activating the phosphoinositide 3 kinase-protein kinase B (PI3K-AKT) signaling pathway. Dose-response relationship studies confirmed the efficacy of ALBP in preventing osteosarcopenia. Further analysis using gut microbiota sequencing, depletion models, and correlation analysis demonstrated that the preventive effects of ALBP are strongly correlated with the gut microbiota, including Bacteroidota, Firmicutes, Desulfobacterota, and Patescibacteria. These results highlight the potential of ALBP as a promising candidate for preventing osteosarcopenia and improving the well-being of the elderly.