Abstract: The present study characterized the pulmonary microvascular architecture in the parenchyma of newborn yak by vascular corrosion cast and scanning electron microscopy in order to explore the distributing patterns of pulmonary microvessels in newborn yak, the mechanisms of the microvascular growth and development during the postnatal period. We found irregular, honeycomb like alveolar capillary network on the cut surface at a low magnification. In some fields of view, the alveolar capillary networks extended incompletely, and the alveolar cavities varied in shape and size. We also found completely expanded alveoli, half expanded alveoli, slightly expanded alveoli and unexpanded alveoli. There were three different forms of alveolar capillary network, including sheetlike, sievelike and weblike network. Also the capillary network in the alveolar septa could be classed into single-layered, double-layered and adjacent capillary networks. In addition, the oriented imprints of the endothelial cell nuclei were found on the surface of the well-expanded capillaries.