Abstract: Objective To investigate the effect of hypoxia on the expression and production of fractalkine (FKN) in cultured rat pulmonary artery smooth muscle cells (PASMCs) and pulmonary microvascular endothelial cells (PMVECs). Methods PASMCs and PMVECs from SD rat were cultured in vitro,and were exposed to hypoxia for 12 h,24 h and 48 h. The expressions of fractalkine mRNA and protein in PASMCs and PMVECs were measured by the methods of in situ hybridization and immunohistochemistry. The fractalkine concentrations in supernatant fluid of cultured PASMCs and PMVECs were measured by enzyme-linked immunosorbent assay. Results ① Compared with the control group, the expression and production of fractalkine in PASMCs did not increase after the treatment of hypoxia for 12 hours (P>0.05), but increased after being treated with hypoxia for 24 hours (P<0.05), and became more significant after 48 hours (P<0.01). ②Compared with the control group, there were no differences of FKN concentrations in supernatant fluid of PMVECs, FKN mRNA and protein levels in PMVECs after being treated with hypoxia for 12 hours, 24 hours or 48 hours (P>0.05). Conclusion Hypoxia stimulates the synthesis and secretion of fractalkine in cultured rat PASMCs.