目的：研究Ｗｉｓｔａｒ大鼠孕第９天胚胎发育的分期。方法：用在解剖显微镜下观察大鼠胚胎于分节前形态学的发育特点去分期。结果：可分５期，第１期，羊膜完全形成但未见神经沟。第２期，前面观可见正中线上的神经沟，侧面观未见神经褶。第３期，神经褶清晰，未见前肠。第４期，未见体节。第５期，体节出现。结论：此种分期方法简便、实用、准确。 Objective: To study the staging of embryonic development on the 9th day of pregnancy in Wistar rats. Methods: To observe the morphological characteristics of preimplantation rat embryos staged under a dissecting microscope. Results: Divided into 5 stages, stage 1, amniotic membrane completely formed but no nerve ditch. No. 2, the front view can be seen in the median nerve groove, side view no nerve fold. No. 3, nerve folds clear, no foregut. No. 4, no body section. No. 5, body section appears. Conclusion: This staging method is simple, practical and accurate.