Objectives: Primary dysmenorrhea (PD) is defined as abdominal pain during menstruation period in the absence of an identifiable pathological lesion. Corydalis tuber (CT) is an herbal medicine that has an excellent effect in relieving pain and convulsions. The purpose of this study is to observe the effect of Corydalis tuber aqueous extracts (CTe) on primary dysmenorrhea. Methods: The rats were injected with estradiol benzoate subcutaneously for 10 days (2.5 mg/kg on the first and 10th days, and 1 mg/kg from the 2~9th day). Oxytocin 1 U/kg was treated by peritoneal injection 1 hour after the last 10th injection of estradiol benzoate. CTe 400, 200 and 100 mg/kg were administered orally, once a day for 10 days at 30 minutes after each estradiol benzoate treatment. The results of CTe were compared to those of IND 5 mg/kg orally treated rats. Results: As results of estradiol benzoate and oxytocin administration, noticeable decreases of body weights and gains, uterus weights were observed with congestion and enlargement of the uterus at gross inspections, and increases of abdominal writhing responses, uterus MDA levels, GSH contents, SOD and CAT activities. However, these oxidative stress mediated PD signs were dose-dependently decreased by 10 consecutive days of oral administration of three different doses of CTe 400, 200 and 100 mg/kg as comparable to those of IND 5 mg/kg in CTe 200 mg/kg. Conclusions: CTe had a significant improvement effect on primary dysmenorrhea in the PD rat model induced by estrogen benzoate and oxytocin.