The effects of Pueraria mirifica (PM) on reproductive organs and fertility of adult male mice were investigated. Male mice were divided into four groups (10 mice/group). Groups 1-3 were orally treated with PM at doses of 0 (PM-0), 10 (PM-10), and 100 (PM-100) mg/kg BW/d in 0.2 mL distilled water, and group 4 was subcutaneously injected with 200 microg/kg BW/d of synthetic estrogen diesthylstilbestol (DES). The treatment schedule was separated into two periods: treatment and posttreatment (8 wk for each period). The PM-10 and PM-100 treatments had no effect on testicular weight, sperm number, and serum LH, FSH, and testosterone levels. Only the PM-100 treatment reduced weights of epididymes and seminal vesicle and the sperm motility and viability. Histopathological examination demonstrated that testis, epididymis, and seminal vesicle were normal in all doses of PM treatment. PM-treated males showed no alterations in mating efficiency and on causing pregnancy of their female partners. DES injection impaired all those parameters. Offspring fathered by the PM- and DES-treated males exhibited neither malformations nor change of body weight gains, and the reproductive organ weights of 50-d old pups were in the normal range. The present data clearly demonstrate that a long-term treatment of PM at doses 10 and 100 mg/kg BW/d, via oral route, does not alter a male fertility and a hypothalamus- pituitary-testis axis. Although PM-100 can cause some moderate impairment, no persistent effects were observed. Most of PM-treated mice increased the mating efficiency after stop treatment.