Abstract: Embryo transfer has potential to increase rates of genetic improvement in domestic farm animals. However, numerous factors may contribute to the efficiency of embryo transfer. We applied 6.5-7.5 d embryos to study factors that may affect the pregnancy rates and development of the Dorper sheep. In the present study, totally 236 embryos were transferred to different recipients in spring and fall. The results showed that the pregnancy rates transferred in fall were significantly higher than that in spring, the birth weights of the kids were not different between spring and fall, but 30 d and 60 d weights from spring were heavier than fall. As far as the recipients, there was no significant difference among the three breeds, in which the pregnancy rates of Zhaotong sheep were the highest, and Hu sheep were better than the small-fat-tailed sheep. The birth and 30 d weights of the kids from big recipients (≥40 kg) were heavier than that from small ones (<40 kg), but there was no significant difference from 60 d kids weights. This indicated that the birth weight of the kids related to the recipients weight, but there was no difference between the developments of the kids. Dorper sheep born in the early autumn, which were transferred in spring, developed much better (P<0.05) than those born in the early spring, which were transferred in fall.