Objective To investigate the expression of interleukin-33/tumor suppressor protein 2 (IL-33/ST2) in peripheral blood of children with mycoplasma pneumonia (MPP) and its clinical significance. Methods From June 2017 to October 2018, 100 children with MPP in Kaifeng Children's Hospital were selected as the study subjects (MPP group), and another 100 healthy children in the same period were selected as the control group.Peripheral venous blood was collected from two groups of children, peripheral blood mononuclear cells (PBMC) and plasma were isolated.The expression of IL-33 was detected by enzyme-linked immunosorbent assay (ELISA), the expression of ST2 protein was detected by immunoblotting (WB), COSMED PFT4 instrument was used to detect pulmonary function in two groups of children.Pearson method was used to analyze the correlation between IL-33 and ST2 protein levels in peripheral blood of MPP children and pulmonary function. Results Compared with the control group, the levels of IL-33 and IL-4, ST2 protein in peripheral blood of MPP children increased significantly (t=9.749, 33.783, 43.890, P<0.05), while the levels of INF-γ, PEF%, FEV1% and FEV1/FVC decreased significantly (t=12.014, 19.860, 20.258, 21.006, P<0.05).Pearson analysis showed that IL-33 and ST2 protein levels in peripheral blood of MPP children were positively correlated with IL-4 level(r=0.537, 0.511), and negatively correlated with INF-γ level, PEF%, FEV1%, FEV1/FVC level (r=-0.660—-0.431, P <0.05). Conclusions IL-33 and ST2 are highly expressed in peripheral blood of MPP children.It may be involved in airway inflammation of MPP by mediating Th2 dominant immune response.