We treated 36 outpatients, suffering from secondary amenorrhea, who had no menstruation or no ovulation for more than 6 months before consulting our clinic. After polycystic ovary syndrome, hyperprolactinemia, and other ovarian disorders that require medical treatment had been ruled out through smear test examinations of the uterine cervix and uterine myoma, ovarian tumor, and endometriosis had been checked for with ultrasonography and serum CA-125, the subjects began to take 6 g/day of black soybean in micropowder form for 6 months (S group). We estimated the ovular improvement of theses patients, observing basal body temperature (BBT) and follicular development with ultrasonography during the menstrual cycle as the indexes for ovulation and compared them with 34 patients with no treatment (C group). In the S group, improved ovulation was seen in 12 patients, four patients became pregnant, and three patients had anovular menstruation within 3 months after starting to take soybean powder. The periods of first ovulation were 66 +/- 12 days. After ovulation started, all subjects had regular menstruations and ovulation, with more than a 7-day high phase in BBT. On the other hand, in the C group, improved ovulation was seen in two patients, and two patients had anovular menstruation. In conclusion, black soybean has the potential to improve the anovular menstrual cycle.