Abstract： Objective To evaluate the changes of the upper airway of the patients with obstructive sleep apnea syndrome (OSAS) before and after operations and to know the effects of operations by MSCT. Methods The upper airway dimensions of 26 patients with OSAS were measured on multiplanar reformatted (MPR), curved-planar reformatted (CPR), volume rendering(VR) images of 16-slice spiral CT. The measurements include the anteroposterior calibres and the areas on the reformatted axial images on the pharyngeal cavity levels, the calibres and the minimum areas in retropalatal and retroglossal regions, the areas of the soft palate and uvula on the reformatted sagittal view with maximum thickness, the maximum wall thickness of the right and left the upper airway on the coronary images, the volume of the upper airway before and after the operations. The measurements were correlated with the polysomnography (PSG) records. The data were analyzed paired-samples t-test and Pearson correlations. Results By comparison, the anteroposterior calibres and the cross-sectional areas on the reformatted axial view of the lower retropalatal region (slice 4) of the upper airway increased significantly after operations. The anteroposterior diameter increased from 5. 9 mm before operations to 12.8 mm after operations, where t = - 5.506, P < 0.05. The areas increased from 51.0 mm~2 before operations to 275.0 mm~2 after operations, where t = -5.011, P <0.05. In the higher retropalatal region (shce 2) of the upper airway, the anteroposterior diameter decresased from 14.8 mm before operations to 9.2 mm after operations, where t = 2.867, P < 0.05. The areas decreased from 241.0 mm~2 before operations to 128.0 mm~2 after operations, where t = 3.087, P < 0.05. The anteroposterior calibres of retroglossal region (slice 7) decreased from 12.7 mm before operations to 10.3 mm after operations,where t = 3.718, P <0.05. The L-R calibres and the minimum areas of of retropalatal increased significantly from 6.4 mm, 33.0 mm~2 before operation to 10.9 mm, 76. 0 mm~2 after operation, where t = -3.413, -2. 216, respectively and P < 0.05. Of the 9 cases whose apnea and hypopnea index (AHI) ≤5 events/hour after operations, the minimum areas of retropalatal region, the anterio-posterior diameter, L-R calibres increased significantly. The areas increased from 41.0 mm2 before operations to 76.0 mm~2 after operations, were t = -4. 932, P <0.05. The anteroposterior calibres increased from 4.6 mm before operations to 6.6 mm after operations, where t = - 7. 308, P < 0.05. The L-R calibres increased from 8.3 mm before operations to 13.6 mm after operations, where t = - 4.320, P < 0.05. Conclusions MPR、CPR、VR of MSCT can evaluate the not only the morphology but the function changes of the upper airways on the OSAS patients. The increasing of the minimum cross-sectional area may be one of the important indications for evaluating operations. The narrowing of the higher retropalatal region of the upper airway after operations should be an alert to the clinicians.