The inhibitory effect of Radix Salviae Miltiorrhizae (RSM) on hypoxic structural remodeling of intra-acinar pulmonary arteries (IAPA) was observed by light and electron microscopy and morphometry. It was found that RSM can not only dilate IAPA and relieve the hypoxic injuries to endothelia cells, but also inhibit the active muscularization of IAPA in the hypoxic animals, suggesting that RSM plays a very important role in inhibiting structural remodeling of IAPA and pulmonary hypertension.