Abstract: Objective To study the relationship between expression of T-helper 17(Th17) cells and asthma in children and to provide references for clinical treatment of asthma.Methods A hospital-based case-control study was conducted during 2014 among 150 asthma patients aged 2-15 years(cases) and 200 gender- and age-matched healthy physical examinees(controls) recruited in Chongqing Municipal Traditional Chinese Medicine Hospital.Pulmonary function, peripheral blood Th17 cells, interleukin-4(IL-4), interleukin-17(IL-17), interleukin-8(IL-8), and interferon-γ(INF-γ) were determined among all participants and correlations between Th17 cell expression and cytokines were analyzed.Results The cases had significantly lower percentage of predicted forced expiratory volume in one second(FEV1%) (68.3±5.9% vs. 87.9±6.1%) and percentage of predicted peak expiratory flow(PEF%) (70.4±6.2% vs. 92.4±6.7%) than the controls(both P<0.001).There were significantly higher levels of peripheral blood Th17 cells(2.48±0.87% vs. 0.26±0.12%), IL-4(166.84±29.45 vs. 68.95±12.37 ng/L), IL-17(5.30±2.14 vs. 2.89±1.70 ng/L), and IL-8(529.46±193.20 vs. 157.97±48.24 pg/L) and lower level of INF-γ(35.16±5.04 vs. 51.49±7.02 ng/L) in the cases compared to those in the controls(all P<0.001).Correlation analysis showed that the level of Th17 cells in peripheral blood was positively correlated with IL-17 level in the cases(r=0.437, P<0.001).Conclusion Th17 cell expression in peripheral blood is higher in children with asthma than in healthy children and the expression may play a role in inflammatory reaction via the mediation of IL-17.