Abstract: Objective To investigate the positive rate of anti-MP IgM + and anti-MP IgG + of Mycoplasma pneumonia(MP) in children with respiratory infection in Shenyang and the relationship betw een MP infection and age,gender,and season.Methods Passive particle agglutination and dot immunofiltration assay(DIFA) were used to detect serum anti-MP IgM and anti-MP IgG.Retrospective analysis was used for the measurement of anti-MP IgM and anti-MP IgG in 7 023 children under the age of 15 years with respiratory infection from Janaury to December,2010.Results The total positive rate of MP in the children was 36.6% (2 569/7 023).The positive rate was 36.1% for anti-MP IgM (2 536/7 023),w ith a significant difference between male and female (33.3% vs 39.5%,P< 0.01).The positive rate was 8.5% for anti-IgG (597/7 023) without significant gender difference(P >0.05).The positive rate of anti-IgM in spring,summer,autumn,and w inter was 29.0%,37.1%,38.9%,and 35.4%,respectively,w ith significant differences among the seasons(P< 0.01).The positive rate of anti-IgM was the highest in autumn and that of anti-IgG was the highest in winter.The positive rate of anti-IgM in the new born,baby,infant,preschool children,and school children was 2.6%,8.3%,20.6%,40.0%,and 44.9%,respectively,and that of anti-IgG was 0%,0.3%,3.5%,11.6%,and 9.7%,respectively,w ith significant differences among the different groups(P< 0.01 for all).Conclusion Mycoplasma pneumonia infection accounts for more than one third of respiratory infection in the children and is the most common in autumn.The children less than one year old have the low est positive rate.The positive rate increases with the age of children and the morbidity is higher in the female.