Abstract: Objective To investigate the prevalent feature of etiology of children with Pneumonia Mycoplasma in Beijing region, and to provide etiology basis for clinical diagnosis of MP. Methods MP-IgM antibody in serum of children patients was detected by indirect immunofluorescence method, and MP positive rate in different gender, age, season and situations of mixed infection with other pathogens infection were then statistical analyzed. Results MP-IgM antibody positive rate in 1985 cases of children patients was 16.52%, and the positive rate between male children (15.55%) and female children (18.13%) had no significant differences（P＞0.05）. MP-IgM antibody positive rate between different age groups had significant differences, in which infant’s group has the lowest (7.09%), and with the age growing, the positive rate increased. Compared with the other groups, the positive rate in group of school age was significantly higher (P＜0.01). The positive rate of IgM antibody was different in different seasons. The positive rate during autumn (27.92%) and spring (18.81%) was significantly higher than that in summer (10.81%) and winter (7.87%). 160 cases out of 328 positively detected cases of MP-IgM were mixed infected with other kind of pathogens (48.78%). 96 cases were mixed infected with one kind of pathogens (29.27%), while 24 cases were mixed infected with two kinds of pathogens (12.20%), and mixed infected with three or more pathogens was 40 cases (7.32%). Conclusion MP infection rate has differences in age and season, and there’s no significant difference between genders of children in this region. The mixed infected rate with other respiratory tract pathogens is high.