Abstract: OBJECTIVE To investigate the role of IL-6/STAT3 signaling pathway in lung function and Th17/Treg cells imbalance in children with Mycoplasma pneumonia. METHODS From May 2021 to Feb. 2022, 150 children with Mycoplasma pneumonia who were treated in Xingtai People's Hospital were selected as the study group, and 50 children who came to our hospital for physical examination during the same period were randomly included as the control group. ELISA was used to detect the levels of interleukin-6 (IL-6), C-reactive protein (CRP), and procalcitonin (PCT); flow cytometry was used to detect Th17 and Treg, and Th17/Treg was calculated; real-time fluorescence quantitative PCR was used to detect STAT3 mRNA expression; pulmonary function indexes of the two groups were detected, such as forced expiratory volume in 1 second (FEV₁), peak expiratory flow rate (PEF) and 1 second rate (FEV₁/FVC). RESULTS Compared with the control group, IL-6, PCT and CRP in the study group were significantly increased (P<0.001); the Th17 percentage and the Th17/Treg ratio in the study group were significantly increased, and the Treg percentage was significantly decreased. STAT3 mRNA in the study group was significantly higher than that in the control group (P<0.001); the PEF, FEV₁% and FEV₁/FVC pulmonary function indexes of the children in the control group were significantly better than those in the study group (P<0.001). CONCLUSION The imbalance of Th17/Treg cells in children with Mycoplasma pneumonia and the increase of IL-6/STAT3 signaling pathway related molecules lead to the decline of lung function in children. It is speculated that the activation of IL-6/STAT3 signaling pathway might trigger the imbalance of Th17/Treg cells, which in turn affected the corresponding cytokine levels, leading to the occurrence and development of Mycoplasma pneumonia.