To study the carotid intima-media thickness （IMT） level of OSA patients of different severity, the proportion of Th17 cells in peripheral blood and the mRNA level of nuclear transfer factor RORγt, and to explore the relationship between Th17 cells and atherosclerosis in OSA patients. Sixty-two patients who underwent respiratory and sleep monitoring were selected and divided into three groups according to the AHI index: 15 patients in the normal control group（AHI<5）, there were 22 cases in the mild group（AHI 5-15） and 25 cases in the moderate and severe group（AHI≥15）. Carotid intima-media thickness（IMT） was measured in all subjects, the ratio of Th17 cells in peripheral blood monouelear cells（PBMC） were analysed by flow cytometry. The expression of RORγt mRNA were detected by real-time polymerase chain reaction. The carotid IMT of patients in the normal control group, the mild OSA group and the moderate to severe OSA group were （0.74±0.21） mm, （1.09±0.23） mm and （1.60±0.30） mm, respectively. The moderate to severe group was higher than the mild group and the normal control group, the difference was statistically significant （<0.01）. The proportion of Th17 in peripheral blood of the three groups was（2.54±0.20）%, （4.34±0.30）%, and （8.27±0.31）%, respectively. The moderate to severe group was significantly higher than the mild group and the control group （<0.01）, the difference was statistically significant. The relative mRNA expression levels of RORγt in the three groups were 0.92±0.24, 2.60±0.59, and 4.93±0.72, respectively. The moderate to severe group was significantly higher than the mild group and the control group （<0.01）, the difference was statistically significant. The proportion of Th17 in peripheral blood and the relative expression of RORvt mRNA were positively correlated with the carotid IMT （ value was 0.80, 0.78, respectively, all <0.01）. Th17 cells differentiation is increased in OSA patients, and Th17 cells are correlated with indicators reflecting the progression of atherosclerosis. Th17 cells may be involved in the development of atherosclerosis in OSA patients.Copyright© by the Editorial Department of Journal of Clinical Otorhinolaryngology Head and Neck Surgery.