Abstract: The object of the present invention is to provide a drug effective in treating or preventing osteoporosis. The present invention discloses a therapeutic or preventive drug for osteoporosis having a compound shown in the formula (1) (wherein R1 is an alkyloxy group with the carbon number of 1 to 4) or a pharmaceutically acceptable salt or ester of said compound in the formula (1) as an effective ingredient. In the compound of the formula (1), a substance in which R1 is CH3O is isotaxiresinol derived from Taxus yunanennsis and showed physiological activities in inhibiting bone resorption and improving bone formation.