Objective To investigate the changes of serum thyroxine level in obstructive sleep apnea-hy-popnea syndrome(OSAHS) patients and to assess the role of serum thyroxine in the development of OSAHS. Meth-ods Polysomnography was used to examine the patients with OSAHS and fasting plasma serum thyroxine level were higher in obese OSAHS patients than in obese controls[ (43.56±3.48)cm vs (38.33±3.08)cm,t =4. 258,P < 0.05 ], in non-obese OSAHS patients than in non-obese control group [ (40.50±1.05 )cm vs (36.17±3.13 )cm, t = 3. 146 ,P < 0.05 ] . The levels of FT3 was (6.35±3.15 ) pmol/L in obese OSAHS patients and ( 4.08±2.37 ) pmol/L in control subjects ( t = 2.203 ,P < 0.05 ). That was ( 3.42±0.57 ) pmol/L in non-obese OSAHS patients related with AHI and microarousal index (r = 0. 500, P < 0.05;r = 0.561, P < 0.05 ), and FT4 was also positively with neck circumference( t = 0.489, P < 0.05 ), TSH level was negatively correlated with neck circumference ( t = - 0.500, P < 0.05 ) and was positively correlated with the percentage of body fat ( r = 0.498, P < 0.05 ). Conclu-sions The FT3 levels are significantly higher in the OSAHS patients than that in control subjects, though all FT3 lev-els are normal, suggesting that there are possibility to have abnormal metabolism. At the same time, FT3 level is posi-tively correlated with neck circumference ,suggesting that the OSAHS patients' higher neck circumference is correla-ted with thyroxine.