Objective To compare the effects of gastric gavage and intramuscular injection of prednisone on the bone mineral density, skeletal biomechanical properties and bone metabolism in rats.Methods A total of 45 SPF rats were randomly divided into three groups:normal group, intragastric administration group, and intramuscular injection group.The normal group, as a control group, was administrated with normal saline 2 mL per day, both the intragastric administration group and i.m.injec-tion group received prednisone 0.5 mg/(kg.d) for 12 weeks.All rats were examined for bone mineral density (BMD) and the level of serum β-CTX and PINP.The femoral cortical biomechanical properties ( elastic load, maximal load, rupturing load) were measured by three point bending test.Results After 12 weeks, compared with the normal group, BMD and elastic load, maximal load, and rupturing load of the femur were significantly decreased.Compared with the intragastric gavage group, BMD was significantly decreased, while the elastic load, maximal load, and rupturing load of the femur were not significantly changed in the i.m.injection group (P＜0.05 for all).Compared with the normal group, the level of serum β-CTX was significantly raised (P＜0.05) and the level of serum PINP was significantly decreased (P＜0.05).Compared with the intragastric gavage group, the level of serumβ-CTX was also significantly raised (P＜0.05), the level of serum PINP was significantly decreased (P＜0.05), the bone trabecula and hemopoietic tissue were obviously decreased, while the adipose tissue increased obviously. Conclusions Both intragastric gavage and intramuscular injection of prednisone affect the level of BMD, skeletal biomechanical properties and bone metabolism.However, i.m.injection of prednisone decreases the BMD and bone strength more significantly, leading to a higher bone turnover with increased bone resorption, and leads to osteoporosis earlier.Our results may suggest that oral administration of prednisone is more safe in clinical treatment.