In order to study the change and significance of serum leptin in obese hypoventilation syndrome (OHS) patients. Serum leptin levels in patients with OHS were studied by enzyme-linked immunosorbent assay (ELISA) and polysomnography.Choose 23 patients in the OHS group, 40 patients with obesity OSA without OHS (obese OSA group), 14 patients without obesity OSA (non-obese OSA group), and simple obesity were selected. 6 cases (simple obesity group) and healthy adults 10 cases (normal control group). The gender, age, neck circumference, waist circumference, BMI and other general data, serum leptin levels and polysomnography parameters were compared among all subjects. Blood gas analysis was performed in OHS group, obese OSA group and simple obesity group, and the results were compared. Correlation analysis of leptin and other related parameters, and analysis of the diagnostic prediction of OHS by indicators such as leptin. The results show that the BMI of the OHS group [(42.6±8.7) kg/m2, P<0.05] and the neck circumference [(45.5±4.7) cm, P<0.05] were significantly higher than the other groups. Younger than other groups [(30 ± 11) years old, P < 0.05]. The serum leptin level in the OHS group [(14.4±1.1) ng/mL] was significantly higher than that in the obese OSA group [(11.9±0.8) ng/mL, P<0.05], and the simple obesity group [(9.3±0.9) ng /mL, P<0.05)], non-obese OSA group [(10.8±0.9) ng/mL, P<0.05] and normal control group [7.0±0.7) ng/mL, P<0.05) There was a significant difference between the groups (P < 0.05). Serum leptin levels and BMI (r=0.38, P<0.01), neck circumference (r=0.35, P<0.01), waist circumference (r=0.37, P<0.01), hip circumference (r= 0.38, P<0.01), PaCO2 (r=0.59, P<0.01), arterial blood HCO3- (r=0.48, P<0.01) and venous blood HCO3- (r=0.29,P <0.01) was positively correlated and negatively correlated with PaO2 (r=-0.45, P<0.01). BMI, neck circumference, waist circumference and serum leptin levels have diagnostic predictive effects on OHS. It is concluded that serum leptin levels in OHS patients are significantly higher than those in obese OSA group and simple obesity group. In addition to obesity, OHS itself can also be a cause of elevated serum leptin levels,Increased serum leptin levels can be used as one of the diagnostic predictors of OHS.