FeNPs were single instilled intratracheally to the male and female parent mice. Two female parent mice died at 4 mg/kg dose during pre-mating period. The body weight gain dose-dependently decreased in male and female parent mice. Iron accumulation was observed in the ovary and the testis of FeNP-treated parent mice. The total sex ratio of the offspring mice increased in FeNP-treated parent group.