Abstract: Thirty-one 3-month-old ♀ Sprague -Dawley rats were randomly divided into 5groups,basal control(group 1,killed at the begining),aging control(group 2),ovariectomized(OVX,group3),OVX with nilestriol treatment group(group 4)and OVX with osthole treatmentgroup(group 5).Group 2 and group 3 ig with water 5 ml·kg^-1 and group 5 ig with osthole 6.7m8· kg^-1, all once a day for 6 d;group4ig with nilestriol 1 mg·kg^-1,once a week.After 12weeks,all rats were killed.The proximal tibiae of rats were processed to undecalcified sections at 20um thickness for histomorphometric analysis.OVX was shown to reduce markedly the trabecular bonemass(%Tb.Ar一59%)due to increase of bone turnover with the result that bone resorption exceededbone formation, as compared with aging controls.In contrast,treatment of OVX rats with Ostholeand nilestriol increased significantly the trabecular area(increased 68%and 274%compared with thatof OVX respectively).Our results indicate that osthole and nilestriol treatment provides protectionagainst osteoporosis in OVX rats.The protective mechanism of osthole and nilestriol involvessupressiOn of bone turnover,but the effects of osthole is lower than that of nilestriol(trabecular areadecreased 55%more in osthole group than that with nilestriol treatment).Our finding may providetheoretical evidence for the clinical use of osthole or nilestriol for treatment and prevention ofosteoporosis.