Objective To evaluate the effects and the molecular mechanism of Liuwei dihuang pills in preventing steroid-induced osteonecrosis of the femoral head (ONFH) so as to provide an expremental basis for preventing ONFH cl inically. Methods Thirty-six adult Kunming mice (weighing 40-50 g, 46 g on average) were randomly divided into three groups (n=12): group A (control group), group B (model group) and group C (prevention group). In groups B and C, ONFHmice models were produced by intraperitoneal injection of horse serum at first (10 mL/kg) and a second injection of horse serum intraperitoneally (5 mL/kg) and prednisolone intramuscularly [45 mL/(kg•day), for 5 days] 2 weeks later. At the same time, the mice in group C were given Liuwei dihuang pills intragastrically [2 g/(kg•day)] and were given normal sal ine [10 mL/(kg•day)] in group B. In group A, mice were given normal sal ine intramuscularly and intragastrically as controls. The animals were sacrificed 2, 4, and 8 weeks after first treatment with prednisone, and femoral heads and l ivers were harvested to do histopathology analysis and apoptosis assay. Results Other mice survived throughout the experiment period except two death at 7 and 11 days after second injection of horse serum intraperitoneally in group B and one death at 24 hours after second injection of horse serum intraperitoneally in group C. The appearance and shape of the femoral head and the surface of cartilages were all normal. The histological observation showed: normal structures of l iver and femoral head were seen in group A at each time point; swell ing l iver cells with small fat vacuole, unclear structure of hepatic cords and narrower sinus hepaticus were seen, the bone trabeculae of femoral head was thin, sparse and collapsed in some regions and the changes became more obvious with time in group B; group C had similar results to group A. The percentage of empty osteocyte lacunae was significantly higher in group B than in groups A and C (P lt; 0.01). The osteoprotegrin expression significantly decreased and the osteoprotegrin l igand expressionsignificantly increased in group B when compared with groups A and C (P lt; 0.01). Apoptosis analysis showed that the apoptosis index in group B was significantly higher than that in groups A and C (P lt; 0.01). Conclusion Liuwei dihuang pills can prevent steroid-induced ONFH by improving l ipid metabol ism, releiving bone lesion, and protecting against cell death.