Abstract: Objective：To study the effects of A20 on the inflammatory response of alveolar macrophages and its regulation mechanism through establishing A20 overexpressing alveolar macrophage cell lines. Methods：Lentivirusmediated expression vector carrying A20 gene was constructed, then it was transfected into rat alveolar macrophage cell lines (NR8383), and the cell lines which stably overexpressed A20 gene were screened and cultured in vitro. Lipopolysaccharide (LPS, 1 μg/mL) was added into the medium to intervene, the culture supernatants and cells were collected 0.5, 1, 2, 4 hours after stimulation, ELISA method was used to determine the activity of cytokines (TNFα, IL1β) and nuclear factor (NFκB). Western blotting method was used to detect A20 protein and nuclear p65 content, and realtime fluorescence quantitative PCR method was used to determine the content of A20 mRNA. Results：After LPS stimulation, the levels of A20 protein and mRNA in A20 overexpression group (A20 group) and the normal control group (VEC group) both increased and reached the peak at 1 h, and then gradually decreased. The A20 level of A20 group was significantly higher than that of VEC group (P＜0.05). Compared with VEC group, the levels of cytokines (TNFα, IL1β) in culture supernatants of A20 group significantly reduced (P＜0.05), and the DNA binding activity of NFκB and nuclear p65 content of A20 group also significantly reduced (P＜0.05). Conclusions：A20 can inhibit the activity of NFκB and the secretion of TNFα and IL 1β, and then inhibit the inflammatory reaction activity of alveolar macrophages, thereby reducing the inflammatory response of acute respiratory distress syndrome (ARDS).