Background: Ligustilide (LIG) has been found to inhibit osteoclastogenesis and promote osteogenesis. However, its impact on osteoporosis remains inadequately understood. This study, therefore, aims to investigate the anti-osteoporotic mechanism of LIG. Methods: Bilateral ovariectomy (OVX) was performed on female rats to simulate estrogen deficiency-induced osteoporosis. Subsequently, LIG was administered in vivo experiments to investigate its effects on osteoporosis in OVX-treated rats. Following the administration of LIG or estradiol (E2), used as a positive control, femoral and lumbar vertebrae specimens were collected for histological analysis, micro-computed tomography, and Western blot. Blood and urine samples were taken for biochemical analysis and enzyme-linked immunosorbent assay. Isolated bone marrow mesenchymal stem cells (BMSCs) were used to explore the effects of LIG on cell activity, osteogenic differentiation, prostaglandin-endoperoxide synthase 2 (PTGS2) expression, and the bone morphogenetic protein (BMP)/contraction of Sma and Mad (Smad) pathway. These cells were transfected with PTGS2 short hairpin RNA (shRNA) and then treated with LIG at different concentrations, followed by alkaline phosphatase (ALP) staining, Alizarin Red S staining, and Western blot. Results: LIG significantly increased serum estrogen levels and uterine weight in OVX-treated rats (p < 0.01) and improved bone morphology, including trabeculae in the femurs and the fourth lumbar vertebrae, with no significant change in body weight. LIG elevated bone mineral density (BMD), trabecular number (Tb.N), and trabecular bone volume/tissue volume (BV/TV) while decreasing trabecular spacing (Tb.Sp) levels (p < 0.05, p < 0.01, and p < 0.001). However, it had an insignificant effect on trabecular thickness (Tb.Th) levels. LIG enhanced serum calcium, phosphorus, ALP, and osteoprotegerin (OPG) levels, while reducing urinary calcium and phosphorus levels, as well as levels of bone resorption indicators (tartrate-resistant acid phosphatase-5b (TRAP-5b) and C-terminal telopeptide of type I collagen (CTX-I)) in the serum of OVX-treated rats (p < 0.05, p < 0.01, and p < 0.001). LIG augmented PTGS2, bone morphogenetic protein 2 (BMP2), and Smad4 expressions in bone tissues of OVX-treated rats (p < 0.01 and p < 0.001). In BMSCs, LIG dose-dependently promoted cell viability, ALP positivity, mineralization, and up-regulated the osteoblast markers (collagen type I alpha 1 (Col1A1), RUNT-related transcription factor 2 (RUNX2)), PTGS2, BMP2, and Smad4 levels (p < 0.05, p < 0.01, and p < 0.001). Conversely, PTGS2 silencing reversed the promoting role of LIG in osteogenesis of BMSCs by inhibiting the BMP/Smad pathway (p < 0.01 and p < 0.001). Conclusion: LIG ameliorates osteoporosis in OVX-treated rats and promotes osteogenesis in BMSCs by targeting PTGS2 to regulate the BMP/Smad pathway.