The objectives is to establish a positive correlation between the serology titer of Mycoplasma pneumoniae and the severity of pneumonia, with an emphasis on severity of disease presentation between two different age groups. The research included 110 children admitted at the Tianjin Medical University General Hospital, Tianjin, China, from May 2010 to October 2010. This study included disease history, clinical examination findings, laboratory investigations including Mycoplasma pneumoniae antibody titer (MP-IgM) level as well as imaging, and duration of in-patient treatment. The results of the parameters were also compared between two age groups: children <5 years old and ≥5 years old. Seventy-six percent of the patients who had severe presentation of the disease had a high titer of MP-IgM and 63% of them were older than five years. Platelet level seems to be a promising indicator of progression of disease. Leukocytosis was present in only 4.5% of the 110 children. The C-reactive protein was significantly raised in those older than five years of age. A significant correlation has been found between the severity of disease and Mycoplasma pneumoniae serology titer level in children suffering from Mycoplasma pneumoniae pneumonia. Keywords: Mycoplasma pneumoniae; MP-IgM; pneumonia in children; thrombocytosis ARTICLE INFO