To study the pathologic changes of palatopharyngeal soft tissues in patients with OSAS.Different analyses have been done on uvular muscles (UM) and/or palatopharyngeal muscles (PPM) in patients with OSAS(n = 27), SS(n = 17) and controls (n = 15). The transverse sections were sequentially stained for HE, myofibrillar ATPase, NADH-TR, Lillie Oil Red-O. Ten specimens were evaluated by transmission electron microscopy(TEM).Patients with OSAS have a significantly smaller percentage of muscle in the uvula than that of SS patients (15.0 +/- 3.0 vs 20.3 +/- 5.5), The percentage of muscle is inversely related to the percentage of fibrous tissue in OSAS group (r = -0.75, Y = 42.6 - 0.64X); The total number and area of muscle fibers, the number and area of type I muscle fibers are significantly lower in OSAS than those in SS (800 +/- 345 vs 1200 +/- 360n; 1.10 +/- 0.56 vs 1.70 +/- 0.60 micron 2; 156 +/- 95 vs 360 +/- 225 n; 920 +/- 350 vs 1365 +/- 540 micron 2 respectively); PPM: The percentage of type I muscle fibers within total muscles and its area are significantly lower in OSAS than those in SS and normal controls(20.5 +/- 4.0 vs 34.5 +/- 4.5 n; 20.5 +/- 4.0 vs 35.5 +/- 4.7; 860 +/- 360 vs 1260 +/- 340 micron 2; 860 +/- 360 vs 1350 +/- 370 micron 2; respectively); the muscles from OSAS patients seemed to show neurogenic alterations. Structurally altered fibers shows myofibrillar loss, increased number of vesicles, and rough Z line and so on.Our finding suggest that the neurogenic functional disturbance of pharyngeal dilator muscles may play an important role in causing the airway collapse in OSAS.