Abstract: Objective: To observe the bone mineral density and the expression of blood serum osteoprotegerin(OPG)/receptor activator of nuclear factor-κB ligand(RANKL) protein in adjuvant arthritis rats.Methods: Thirty SD rats were randomly divided into normal control group,model 1 group and model 2 group.Except the normal control group,other rats were made of adjuvant arthritis model.At the 21st day,the bone mineral density of the whole right side of the tibia and about 1 cm from the distal tibia called interest region in model 1 group were detected with dualenergy X-ray absorptoimetry.At the 28th day,the bone mineral density of the whole right side of the tibia and about 1 cm from the distal tibia called interest region in model 2 group and normal group were detected.At the same time,the expression of blood serum OPG/RANKL of adjuvant arthritis rats was inspected by enzyme-linked immuno sorbent assay.Results: The bone mineral density of interest region of model 1 group were lower than that of normal group(P<0.01).The interest region of model 2 group significantly reduced compared with the normal and model 1 groups(P<0.01).The overall right tibia bone mineral density had no significant difference(P>0.05).The expression of blood serum OPG,RANKL and the OPG/RANKL ratio in model 1 and model 2 group were significantly different with the normal group(P<0.01).At the same time,the expression of blood serum OPG,RANKL and the OPG/RANKL ratio in model 2 were significantly different with model 1 group(P<0.01).Conclusions: Adjuvant arthritis rats lost distal tibial bone earlier than the whole tibial.The blood serum OPG expression is decreased,the blood serum RANKL is increased,and the ratio of OPG/RANKL is decreased after modeling 21 days and 28 days.