Objective:To explore the expression of microRNA(miRNA) let-7c and its function in chronic obstructive pulmonary disease(COPD) and alveolar macrophage cells.Methods:Real time PCR was performed to detect the expression of miRNA let-7c in the lung tissue of COPD patients and COPD model in mice.MiRNA let-7c was overexpresscd in alveolar macrophages isolated from mice and its effect was measured by the production of pro-inflammation cytokines and the protein level of signal transducer and activator of transcription 3(STAT3) as well as phosphorylation level of STAT3 after LPS stimulation.Luciferase assay was used to detect the binding of miRNA let-7c and 3’UTR of STAT3.Results:MiRNA let-7c expression was significantly lower in patients with COPD compared with control group,and the similar result was found in COPD mice and LPS stimulated alveolar macrophages.Overexpression of miRNA lct-7c in alveolar macrophages inhibited LPS-induced increasing of tumor necrosis factor alpha,interleukin-6 and interleukin-1β.Luciferase assay showed STAT3 was a targeting of miRNA lct-7c in alveolar macrophages.Conclusions:MiRNA lct-7c low expression in COPD can regulate inflammatory responses by targeting STAT3 in alveolar macrophage,which may provide a new target for COPD treatment strategies. Objective: To explore the expression of microRNA (miRNA) let-7c and its function in chronic obstructive pulmonary disease (COPD) and alveolar macrophage cells. Methods: Real time PCR was performed to detect the expression of miRNA let-7c in the lung tissue of COPD patients and COPD model in mice. MiRNA let-7c was overexpresscd in alveolar macrophages isolated from mice and its effect was measured by the production of pro-inflammation cytokines and the protein level of signal transducer and activator of transcription 3 (STAT3) as well as phosphorylation level of STAT3 after LPS stimulation. Luciferase assay was used to detect the binding of miRNA let-7c and 3’UTR of STAT3.Results: MiRNA let-7c expression was significantly lower in patients with COPD compared with control group, and the similar result was found in COPD mice and LPS stimulated alveolar macrophages. Overexpression of miRNA lct-7c in alveolar macrophages inhibited LPS-induced increasing of tumor necrosis factor alpha, interleukin-6 and Interleukin-1β.Luciferase assay showed STAT3 was a targeting of miRNA lct-7c in alveolar macrophages. Conclusions: MiRNA lct-7c low expression in COPD can regulate inflammatory responses by targeting STAT3 in alveolar macrophage, which may provide a new target for COPD treatment strategies.