Objective:To study the effect of simvastatin therapy on bone density and metabolism in rats with osteoporosis. Methods:Forty female Wistar rats were randomly divided into four group: control group-A (sham operation group), ovariectomized group-B(OVX), OVX with oestrogen treatment group-C and OVX with simvastatin treatment group-D. Thirty days after surgery, oestrogen replacement therapy(nilestriol 1 mg/(kg?d), ig once a week for 12 weeks) in group-C and simvastatin therapy(with simvastatin 5 mg/(kg?d), ig once a day for a week, paused for two weeks,and given for another one week,until 12 weeks)in group-D.After 12 weeks, all rats were sacrificed. On the 12th day and the 4th day before sacrifice,all rats received subcutaneous injections of tetracycline as in vivo label. The proximal tibiae of rats were processed to undecalcified sections and stained with HE or Von Kossa.The microarchitecture was studied by bone histomorphometry. Results:Osteoporotic changes in proximal tibiae were observed in all ovariectomized rats and not in sham-operated rats. There was significant difference in static parameters (%Tb.Ar, Tb.N,Tb.Sp) comparing group C or D with group B respectively(P