To evaluate the effects and safety of varying doses of Guizhi Fuling capsule on treating primary dysmenorrhea. From August 2010 to March 2011, 240 subjects (aged 18-30) with primary dysmenorrheal, were enrolled in 8 sites. They were randomized into Guizhi Fuling capsule high dose group, low dose group and placebo control group, 80 cases in each group. These patients were treated for three consecutive menstrual cycles, then were followed up in another three consecutive menstrual cycles. Visual analogue scales (VAS) was used to determine the pain intensity. During the treatment, the high-, low-dose and placebo groups efficiency on pain relief are 68.42%, 67.57% and 47.89% respectively. Guzhi Fuling (included high- and low- dose group) significantly relieves the pain compared to placebo. In follow-up, Guzhi Fuling groups are still superior to the placebo group (73.68%, 72.97% and 53.52%). During the treatment, pain duration reduces 57.88% in high dose group, while 46.17% in low dose group, and 30.40% in placebo group. In follow-up, pain lasting time decrease 67.93%, 53.56%, 47.46%, respectively. Guizhi Fuling significantly reduces the pain duration compared to placebo and high-dose is better than low-dose. The efficacy of Guzhi Fuling (high- and low-dose) displays certain dosage-effect relationship. Among these group, no serious adverse event was reported. Guizhi Fuling capsule at high or low dose significantly relieves the pain, improves symptoms, reduces the duration of pain, and has a better overall treatment effect and long-term treatment effect in patients with primary dysmenorrhea.