Objective:To investigate the changes of C1q tumor necrosis factor related protein 12 (CTRP12) in patients with obstructive sleep apnea hypopnea syndrome (OSAHS)with different severity. Methods:A total of 120 cases were selected from Southeast University Affiliated Hospital,Jiangyin City People’s Hospital,Chest Hospital Sleep Respiration Monitoring Center by polysomnography (PSG) monitoring,and divided into the OSAHS group and the non OSAHS group. The OSAHS group was divided into the light,medium and severe groups according to apnea hypopnea index (AHI),and each group was divided into the obesity,overweight and normal weight groups according to body mass index (BMI). CTRP12 level,AHI,the lowest oxygen saturation,BMI,blood lipid,blood sugar index in OSAHS patients were detected to understand the role of CTRP12 in OSAHS. Results: In BMI and OSAHS-matched patients of each group,the levels of CTRP12 before sleep and after wake up had no statistical difference;in BMI-matched groups,CTRP12 levels before sleep and after wake up of severe OSAHS patients were significantly lower than those of non OSAHS,light OSAHS,and medium OSAHS patients. CTRP12 levels in light and medium OSAHS patients with normal weight were significantly lower than those in non OSAHS patients;in OSAHS-matched groups,CTRP12 levels of obese patients before sleep and after wake up were significantly lower than those of patients with normal weight;plasma CTRP12 level of OSAHS patients was related to AHI,BMI,neck circumference,percentage of time when oxygen saturation lower than 90%(SLT90%),triglyceride,fasting blood glucose,lowest arterial O2 saturation(LSaO2),and mean arterial O2 saturation(MSaO2). The CTRP12 level was decreased when AHI,BMI,neck circumference,SLT90%,triglyceride,fasting blood glucose increased,and was increased when LSaO2 and MSaO2 increased. Conclusion:The level of CTRP12 was decreased when OSAHS patients with more severe disease and heavier body weight;OSAHS patients plasma CTRP12 level was negatively correlated with AHI,BMI,neck circumference,SLT90%,triglyceride,fasting blood glucose and positively related with LSaO2 and MSaO2.