The plateau pika (Ochotona curzoniae), one of the endemic rodents inhabiting in Qinghai-Tibet plateau, has adapted well to extreme hypoxic and cold environments. Blunted hypoxic pulmonary vasoconstriction (bHPV) plays an important role on preventing plateau pika from injury induced by hypoxia. To investigate the histochemical basis of bHPV, we examined the structural morphology and immunohistochemistry of pulmonary microvessels from the fetus, pups and adults plateau pikas. The results with Kunming mouse as the comparison species showed that the double elastic lamina was less than 25% of the circumference, suggesting there is no significant muscularization of the pulmonary microvessels (10-200μm in diameter) in plateau pika against hypoxia stress, as the ratio of medial thickness to external diameter (MT/ED) of pulmonary microvessels (of 10-50, 50-100 and 100-200μm diameter) decreased in response to the prolonged hypoxia exposure in plateau pika. In the adults, plateau pika showed a lower MT/ED10-50 than Kunming mouse did (P <0.05), but no significant difference was found in MT/ED50-100 and MT/ED100-200 between two species. In pulmonary arteriole of 10-50μm diameter, higher ratio of microvascular staining with α-SMA to microvascular staining with CD31 (SMC/EC) was detected over time in plateau pika and Kunming mouse. In comparison to Kunming mouse, obviously lower SMC/EC (P < 0.01) was observed in plateau pika at each developmental period. These results suggest that a decrease in development of smooth muscle cells in pulmonary microvessels of 10-50μm diameter probably play an important role in blunting hypoxic pulmonary vasoconstriction in plateau pika.