This experiment was undertaken to investigate the effect of administration of Agyoju or Mokhyang on the maintenance of pregnancy, delivery and sex ratio in the mice in different gestation periods. Adult female mice were administered orally at three different periods, from ovulation to implantation (Exp.1), from post-implantation to organogenesis (Exp.2), and from fetal growth to parturition (Exp.3). In Experiment 1, number of fetus implanted and mean body weight were not significantly different. However, the delivery of male offspring was significantly increased in Agyoju and Mokhyang administrated groups than control group. In Experiment 2, the number of fetuses implanted, live offsprins and their body weight at delivery were significantly increased in the Agyoju administered group than Mokhyang and control groups. In Experiment 3, the number of live offspring and sex ratio were not different in both treatments and control group. However, mean body weight at delivery was significantly increased in both treatment groups than that of control group. These results suggest that 1) Agyoju and Mokhyang have beneficial effects in maintenance of pregnacy, and that 2) The action of unknown component(s) in Agyoju may be related to selection of male spermatozoa for fertilization in vivo, and that 3) the administration of Agyju of Mojhyang during mid-and late-pregnance periods were shown the increment of body weight of live offspring without decrease of litter size.