Wedelia calendulacea Less., a perennial herb containing isoflavanoids, is used in liver disorders, uterine hemorrhage and menorrhagia. Osteoporosis in women occurs mainly due to estrogen deficiency following menopause. Studies indicate that isoflavones are estrogenic enough to promote bone formation. Our study was aimed to investigate the antiosteoporotic effect of the ethanol extract of W. calendulacea in the ovariectomized rat model of osteoporosis, at two different dose levels of 500 and 750 mg/kg/body wt. day. The findings, assessed on the basis of biomechanical and biochemical parameters, showed that the ethanol extract of the plant had a definite protective effect. This was further supported by the histopathological studies. Phytochemical investigation revealed the presence of isoflavones and wedelolactone, which are known to act as phytoestrogens and may be responsible for the antiosteoporotic activity. © 2005 Elsevier GmbH. All rights reserved.