Objective To analyze the clinical features and the plasma secretory leukocyte proteinase inhibitor (SLPI) levels in children with Mycoplasma pneumoniae pneumonia (MPP). Methods Clinical data and plasma SLPI levels of 136 children with MPP were retrospectively analyzed. Results From July 2011 to June 2013,136 children (male 80, female 56) with MPP were included in the study. The onset ages of all children ranged from 11 months to 14 years (mean age, 6.2±3.0 years), and 82.4%of the cases were at the age of 4 to 14 years. One hundred and twenty six cases (92.7%) with long-last high fever, 83.8%with cough, 74.3%with rale were found in the study. Small or large patchy shadows in chest X-ray radiography were found in all the cases. At the acute phase, 72.1%with low white blood cell count, 59.6%with normal neutrophil cell and 63.2%with higher high sensitive C-reactive protein (hs-CRP) were observed. The SLPI level at the acute phase in 85 cases was (9.3±8.8) ng/ml, which was signiifcant lower than that at the convalescent phase (11.8±8.0 ng/ml, Z=3.08, P=0.002). Conclusions The clinical features of MPP are usually presented with high fever, cough, higher hs-CRP, normal or lower white blood cell and neutrophil cell count, small or large patchy shadows in chest X-ray radiography. The plasma SLPI level at the acute phase was signiifcantly lower than that in convalescent phase in children with MPP.