【Abstract】 Objective To explore the changes in levels of serum Creactive protein (CRP), procalcitonin (PCT) and erythrocyte sedimentation rate (ESR) in children with Mycoplasma pneumoniae pneumonia (MPP) and their relationship with MPP severity. Methods The clinical data of 138 MPP children who were diagnosed and treated in pediatrics department of the hospital from June 2017 to May 2019 were retrospectively collected. According to disease severity before treatment, they were divided into severe group (62 cases) and mild group (76 cases). The levels of serum CRP, PCT and ESR before and after treatment were compared and analyzed between the two groups. And their relationship with MPP severity was analyzed. According to the prognosis after 1 course of treatment, they were divided into good prognosis group and poor prognosis group. The levels of serum CRP, PCT and ESR were compared between the two groups. Results Before treatment, levels of serum CRP, PCT and ESR, scores of modified British Medical Research Council Dyspnea Scale (mMRC) and clinical pulmonary infection score (CPIS) in severe group were significantly higher than those in mild group (P＜0.05). After treatment, the above mentioned indexes in both groups were significantly decreased (P＜0.05), which were still significantly higher in severe group than mild group (P＜0.05). Before treatment, the percentage of CT normal lung density volume in severe group was significantly lower than that in mild group (P＜0.05). After treatment, the percentage of CT normal lung density volume in both groups was significantly increased (P＜0.05), which was significantly higher in severe group than mild group (P＜0.05). Spearman correlation analysis showed that serum CRP, PCT and ESR levels were positively correlated with CPIS and mMRC scores in MPP children (P＜0.05), while negatively correlated with the percentage of CT normal lung density volume (P＜0.05). Serum CRP, PCT and ESR in good prognosis group were significantly lower than those in poor prognosis group (P＜0.05). COX multivariate analysis showed that serum CRP, PCT and ESR were closely related to prognosis (P＜0.05). Conclusion The levels of serum CRP, PCT and ESR are positively correlated with disease severity in MPP children, which are of certain correlation with their prognosis.