Objective To investigate the role of T helper 17 ( Th17) cells and CD4 + CD25 + Foxp3+regulatory T cells ( Treg) in the pathogenesis of asthma in a mouse model. Methods Twenty-four BALB/ c mice were randomly divided into an asthma group and a normal control group, with 12 mice in each group.Asthma model was established by ovalbumin sensitization and aerosol challenge in the asthma group. Airway reactivity was measured by plethysmography. The total and differential cell counts in bronchoalveolar lavage fluid ( BALF) were measured. The ratio of Th17 and Treg cells to mononuclear cells in the spleens of mice were detected by flow cytometry. The levels of IL-17 and IL-10 in BALF and lung homogenates were measured by ELISA. Results The bronchial provocation test showed that the average lung resistance increased remarkably in the asthma group. In spleens of the asthmatic mice, the percentage of Th17 cells was significantly higher [ ( 5.68 ±1. 99)% vs ( 2.80 ±0. 82) %, P lt; 0. 01] , and the percentage of Treg cells was significantly lower [ (2.88 ±0. 46) % vs ( 6.10 ±2.44) % , Plt; 0. 01] , with the ratio of Th17 to Treg significantly increased( 1. 93 ±0. 41 vs 0. 50 ±0. 15,P lt;0. 01) . In BALF and lung homogenates of the asthma group, the level of IL-17 was significantly higher[ ( 22. 37 ±3. 00) pg/mL vs ( 11. 42 ±2. 15) pg/mL, ( 52. 93 ±5. 39) pg/mL vs ( 19. 38 ±2. 65) pg/mL, both Plt; 0. 01] , and the level of IL-10 was significantly lower[ ( 6. 05 ±1. 25) pg/mL vs ( 14. 23 ±2. 94) pg/mL, ( 9. 33 ±1. 79) pg/mL vs ( 21. 40 ±2. 44) pg/mL, both P lt; 0. 01] compared with the control group.Conclusion The imbalance of Th17/ Treg plays an important role in the pathogenesis of asthma.