Abstract: Objective To study the role of thymus activation regulated chemokine (TARC) in Mycoplasma pneumoniae caused asthma in children. Methods Seventy three children with acute pneumonia were included in this study (excluding the children with bronchial asthma). At the time of admission, venous blood samples were collected from the children to detect MP-IgM with passive hemagglutination method and IgM antibodies of other 7 respiratory pathogens with indirect immunofluorescence (IIF). A part of the serum was stored at -70 ℃. Throat swabs were collected to detect MP-DNA with quantitative RT-PCR. According to the clinical diagnosis of Mycoplasma pneumoniae infection and serum MP-IgM or MP-DNA copy number of induced sputum, the children with pneumonia were divided into MP infection group and non MP infection group. In convalescence phase, the venous blood samples were collected from the children with asthma attack; and the serum was stored at -70 ℃. The level of TARC in serum was detected with enzyme linked immunosorbent assay (ELISA). The differences in serum TARC level between the MP infection group and non MP infection group and between acute phase and convalescence phase were analyzed. Results The attack rate of asthma was higher in MP infection group than in non MP infection group, the difference had no statistical significance (2=4.44, P=0.04). The level of TARC was higher in MP infection group than in non MP infection group, the difference had statistical significance (t=4.01, P=0.00). In MP infection group, the children with asthma had higher level of TARC than those with and without asthma in non MP infection group, the differences had statistical significance (t=2.62, P=0.01; t=5.21, P=0.00), and the children without asthma had higher level of TARC than those without asthma in non MP infection group, the difference was statistical significant (t=2.07, P=0.05). In both MP infection group and non MP infection group, the levels of TARC in children with asthma were higher than those in children without asthma, the difference was statistical significant (t=2.11, P=0.04; t=2.03, P=0.05).The level of TARC in children with asthma in convalescence phase was lower than that in those in acute phase, the difference was statistical significant (t=4.69, P=0.00; t=2.37, P=0.05). Conclusion TARC plays an important role in the onset of MP infection induced asthma.