Objective:To investigate whether lipopolysaccharide (LPS) combined with adenosine triphosphate (ATP) activates Nod-like receptor pyrin domain-containing protein 3(NLRP3) inflammasome in human pulmonary artery endothelial cells (HPAECs), and the underlying mechanism. Methods: HAPECs were stimulated by LPS with or without ATP to establish inflammation damage model. Cell vitality was assessed by cell counting kit-8. The levels of IL-1β and IL-18 in supernatant were analyzed by ELISA. The expressions of caspase-1, p-p38 and p-p65 were determined by Western blot. Reactive oxygen species (ROS) was detected by DCFH-DA fluorescent probe. Cell apoptosis was evaluated by annexin V and PI staining assay. Results: LPS alone had no effects on HPAECs. By combined with ATP, LPS significantly inhibited cell viability. The levels of IL-1β and IL-18 in supernatant, the expressions of caspase-1, p-p38 and p-p65 in cytoplasm, the concentrations of intracellular and extracellular ROS as well as cell apoptosis were up-regulated in HPAECs activated by LPS combined with ATP. These effects were inhibited by ROS scavenger N-acetylcysteine. Conclusion: High level ROS plays an important role in LPS combined with ATP-induced NLRP3 inflammasome activation as well as apoptosis of HPAECs.