Detailed observations of the growth process of the embryos and fetuses (hereafter, referred to as just fetus) of 6 pregnant Beagle bitches (14-27 months old) was carried out using ultrasonography. From daily measurements of the transversal diameter of the fetal abdomen, diameter of the fetal head and diameter of the fetal heart, significant growth curves (secondary regression equations) were obtained from the day of gestation and the measured values (p < 0.01). The results of this study showed that this method can be applied to estimate the gestation age of dogs in cases when the mating day is unknown, and determine the state of fetal growth.