AIM: To investigate the expression of phosphatidylinositol 3-kinase (PI-3K) during the proliferation of the hypoxic pulmonary arterial smooth muscle cells(PASMC). METHODS: The cultured PASMC was divided into two groups: serum-free medium (SFM) group and 48 hours hypoxia (H48h) group. Immunohistochmistry(IHC) and Flowcytometer(FCM) were used to detect the cultured PASMC. RESULTS: The positive expression of PI-3K p110 existed in both cultured PASMC groups. The staining intensity in H48h group (0 1891?0 0301) was significantly stronger than that in SFM group (0 1025?0 0164, P