Catalpol, an iridoid glycoside obtained from various natural sources, has many biological functions. However, its ovarian failure-resistant effect has scarcely been studied. The present study used senile 14-month-old Sprague-Dawley female rats to examine the in vivo ovarian failure-resistant activity of catalpol. Daily oral graded doses of catalpol (1, 3, or 5 mg/kg/d) for 4 weeks significantly increased the levels of serum 17β-estradiol (E2) and progesterone (P4) but reduced follicle-stimulating hormone and luteinizing hormone levels. Electron microscopic analysis and flow cytometry showed that catalpol significantly retarded apoptosis of the ovarian granulocytes of the rats. These findings suggest that catalpol works on the sex organs by nourishing ovarian tissues and improving both the quality and quantity of follicles, thus leading to rebalanced E2 and P4 levels in aged rats so that catalpol has a direct in vivo antiaging effect on the rat ovarian system.