The teratogenicity study of fosfomycin-Na (FOM-Na) was undertaken in Wistar rats and New Zealand white rabbits. Rats were treated intraperitoneally at dose levels of 125, 250, 750 and 1,500 mg/kg/day from day 7 to day 17 of gestation, and rabbits were treated intravenously at dose levels of 80, 100, 200, 400 and 800 mg/kg/day from day 6 to day 18 of gestation. In the case of rats, two-thirds of pregnant mothers in each group was sacrificed on day 20 of gestation and then their fetuses were examined for external, visceral and skeletal observation. The remaining mothers were allowed to deliver naturally, and then their offsprings were examined for postnatal development. In the case of rabbits, all pregnant mothers were sacrificed on day 29 of gestation and their fetuses were examined. Body weight of rat mothers during gestation were decreased and 4 mothers were dead until day 20 of gestation in the maximum dose. In this dose, foetal toxicity was recognized too. However, external, visceral and skeletal anomalies related with FOM-Na treatment were not observed in all groups. No effect on development of offsprings was observed. No effect of treatment of FOM-Na to rabbits was found except foetal body weight was slightly decreased in the maximum dose.