Objective To explore the correlation between serum vitamin D level and extra-pulmonary involvement in children with mycoplasma pneumoniae pneumonia (MPP),in order to provide theoretical evidence for clinical assessment. Methods Totally 158 MPP children admitted to Yulin First Hospital from December 2015 to December 2017 were enrolled in this study,and were divided into extra-pulmonary involvement group (n=56) and non extra-pulmonary involvement group(n=102).And all children were classified into normal vitamin D group,insufficiency group and deficiency group based on vitamin D level.Prevalence rates of extra-pulmonary involvement in different groups of vitamin D levels were compared. Results Compared with non extra-pulmonary involvement group,duration of fever in extra-pulmonary involvement group was much longer.And the levels of WBC,ESR,CRP,D-D were higher,while serum vitamin E and 25-hydroxyvitamin D[25-(OH)D] levels were significantly lower in extra-pulmonary involvement group(P<0.05).There were statistically significant differences on the prevalence rate of extra-pulmonary involvement children in different vitamin D level groups (P<0.05).Multivariate Logistic regression analysis showed that vitamin D insufficiency (OR=1.955,95%CI:1.479-4.233,P=0.006) or deficiency(OR=2.360,95%CI:1.687-8.215,P＜0.001) were independent risks factor of extra-pulmonary involvement (P<0.05).ROC curve analysis showed that the area under curve (AUC) of serum 25-(OH)D level predicting extra-pulmonary involvement was 0.840,and its sensitivity and specificity were 81.45% and 87.76% respectively.The optimal cut-off point of serum 25-(OH)D level was 22.48 ng/ml. Conclusions vitamin D insufficiency or deficiency significantly increase the risk of extra-pulmonary involvement in MPP children,and may be the predictive factor for its occurrence independently.So vitamin D level should be closely monitored to evaluate prognosis of MPP children in clinical practice