Objective: To explore the role and the mechanism of Th17/Treg in obstructive sleep apnea hypopnea syndrome (OSAHS). Methods: A total of 100 patients who completed polysomnography (PSG) in the sleep lab of Affiliated Wujiang Hospital of Nantong University from Mar. 2015 to Apr. 2016 were enrolled and divided into four groups (primary snoring as the control group, mild OSAHS, moderate OSAHS and severe OSAHS) according apnea hypopnea index (AHI). The proportion of Th17, Treg (of CD4+ T cells) and the expression of interleukin (IL)-17A, IL-6 were detected and the relevant data were analyzed by the correlation analysis and the multiple stepwise regression analysis. Results: Compared with the control group, the OSAHS patients had higher Th17% [(1.36±0.46)%, (1.68±0.30)%, (2.23±0.03)% vs (1.02±0.22)%], Th17/Treg [(0.22±0.07), (0.28±0.10), (0.29±0.00) vs (0.13±0.03)], IL-17A [(2.53±0.89), (2.99±1.96), (7.77±1.63) vs (1.45±0.78) ng/L], IL-6 [(6.14±4.37), (9.41±4.66), (12.58±6.65) vs (5.44±3.13) ng/L] and lower Treg% [(7.57±0.16)%, (6.46±1.57)%, (6.10±1.19)% vs (8.02±1.45)%] (all P<0.05). A positive correlation could be seen between Th17%, Th17/Treg, IL-17A, IL-6 and AHI, oxygen desaturation index (ODI) respectively, there was a negative correlation between Th17%, Th17/Treg, IL-17A, IL-6 and the lowest oxygen saturation (SpO2) (all P<0.05). The proportion of Treg had a negative correlation with AHI or ODI and a positive correlation with the lowest SpO2 (all P<0.05). The lowest SpO2 was the most important factor which could influence Th17%, Treg% and the radio of Th17/Treg. Conclusions: There is an imbalance of Th17/Treg in OSAHS. Therefore, Th17 and the relevant inflammatory cytokines may be involved in the occurrence and development of OSAHS.