Abstract: Objective　To analyze the clinical characteristics of Mycoplasma pneumoniae pneumonia in children under 2 years old. Methods The clinical features and treatment outcomes were analyzed in 57 children under 2 years old and compared with 153 children more than 2 years old. Results Compared with children more than 2 years old, in children under 2 years old, the number of cases with fever was fewer, the fever peak was lower and the lasting time was shorter. However, in children under 2 years old, the severe pulmonary signs were more common, the incidence of wheeze was higher, meanwhile, the count of white blood cells (WBCs) was significantly increased, more small pieces of fluff shadow was showed on chest X-ray, and the pulmonary complications were fewer, less corticosteroid was needed for treatment. After one-week therapy, the chest X-ray shadows were disappeared in most of children. Complications out of lungs, such as rash, liver function damage and cardiac damage can be found in both groups and no significant difference (P>0.05). Conclusions mycoplasma pneumoniae pneumonia in children under 2 years old had the characteristics of mild symptoms, severe pulmonary signs, few pulmonary complications, light systemic inflammations and mild radiological changes.