Objective To determine the effect of fudosteine on the percentages of Th1 and Th2 cells and the serum levels of interferon-γ (IFN-γ) and interleukin-4 (IL-4) in severe obstructive sleep apnea syndrome (OSAS) patients. Methods Fifty-seven severe OSAS in- and out-patients and 20 simple snorers who were treated in the Wuxi People’s Hospital from April 2013 to December 2014 were recruited in this study. All the participants were male, and aged from 55 to 76 (67.0±6.4) years. According to apnea hypopnea index (AHI), the cohort was divided into 3 groups, that is, control group (simple snorers, AHI≤5, n＝20), OSAS group (AHI＞40, n＝28) and OSAS＋fudosteine group (AHI＞40, taking fudosteine for 2 weeks, n＝29). The proportions of Th1 and Th2 cells were detected by flow cytometry, while the serum contents of IFN-γ and IL-4 were evaluated by ELISA. Results There was no significant difference in the age and body mass index (BMI) among the 3 groups (P＞0.05). Compared with the control group, the proportion of Th1 was increased obviously in OSAS group [F(2,74)＝85.06, P＜0.01], meanwhile, the level of IFN-γ (Th1 related cytokine) was also significantly elevated [F(2,74)＝131.4, P＜0.01]. Compared with OSAS group, both the proportion of Th1 [F(2,74)＝85.06, P＜0.01] and level of IFN-γ [F(2,74)＝131.4, P＜0.01] were decreased markedly in OSAS＋fudosteine group. However, there was no statistical difference in the proportion of Th2 cells [F(2,74)＝2.66, P＝0.08] and serum level of IL-4 [F(2,74)＝2.29, P＝0.11] among the 3 groups. Conclusion Th1 cells are activated obviously in the patients with severe OSAS, and more Th1 related cytokines are secreted, while, no obvious alternations of Th2 cells and related cytokine are found. Fudosteine inhibits the excessive activation of Th1 cells and excessive secretion of Th1 related cytokine.