Endocrine disruptors are known to have the potential to interfere with reproductive systems. It has been reported that early embryogenesis was affected by estrone in chicks. In the present experiment, the effects of estrone on early embryos during pre-organogenesis were investigated to evaluate the effects and toxicities of endocrine disruptors. Mouse embryos at day 6.5 of gestation were recovered and cultured for 48 h in a medium at a concentration of 10 or 100 ng/mL estrone. After cultivation, the embryos were measured for the diameter of the total conceptus, including both embryo and yolk sac, and head-tail length. The diameters of conceptus in both treated and control groups were not significantly different, but the growth of the conceptus was slightly inhibited in the 10 ng estrone group. The lengths of embryos were significantly decreased in the 10 and 100 ng/mL estrone-treated groups. Thus, estrone affected embryo growth at pre-organogenesis, suggesting that the endocrine disruptor could also have some effects and toxicities on mouse embryogenesis.