The present experiments examined the effects of electrical stimulation of the superior ovarian nerve (SON) and the ovarian plexus nerve (OPN) on the ovarian estradiol secretion in rats. The rats were anesthetized on the day of estrus, and the ovarian venous blood was collected intermittently. The secretion rate of estradiol from the ovary was calculated from differences in the estradiol concentration between ovarian venous plasma and systemic arterial blood plasma, and from the flow rate of ovarian venous plasma. Either an SON or OPN, ipsilateral to the ovary from which ovarian venous blood was collected, was electrically stimulated at a supramaximal intensity for C-fibers. The secretion rate of estradiol was significantly decreased by 47 ± 6% during SON stimulation, but it was not significantly changed during OPN stimulation. These results suggest that autonomic nerves, which reach the ovary via the SON, have an inhibitory role in ovarian estradiol secretion.