Objective: To investigate the relationship between Apelin and OSAHS. Method: According to apnea-hypopnea index (AHI) and body mass index (BMI), We’ve selected the OSAHS group (89 cases) and non-OSAHS group (30 cases), from the patients ongoing monitoring of sleep apnea in the sleep disorder center in ZhongDa Hospital from January 2008 to December 2009. According to BMI, the group of data is divided into obese, overweight, normal weight, in the mean time, each obese, overweight, normal weight sub-group of OSAHS group is divided into mild, moderate and severe three ones according to AHI. All subjects received polysomnography monitoring, and plasma apelin (ng / ml) levels using enzyme-linked immunoassay. Results :In the non-OSAHS group and mild to moderate OSAHS group, the obese plasma apelin levels were significantly higher than overweight, the overweight were also significantly higher than the normal weight ones. Yet in the severe OSAHS group, there was no significant difference among the obesity group, overweight group and the normal weight group (P> 0.05). OSAHS groups were significantly higher than the groups without OSAHS of the same weight degree. Plasma concentration of apelin was significantly higher in patients of moderate and severe OSAHS groups than in the mild OSAHS group. But there is no significant difference been explored between the moderate OSAHS group and severe OSAHS group. Plasma apelin level was significantly correlated positively with AHI (r=0.581, P <0.01) and BMI (r=0.392, P <0.01), but correlated negatively with LSaO2 (r=-0.320, P <0.01) and MSaO2 (r=-0.495, P <0.01). Conclusion : The plasma apelin levels increased in OSAHS patients and obese patients . Apelin may play an important role in the occurrence and development of OSAHS.