Abstract： Objective To observe the differences of endogenous cannabinoid system(ECS) synthetic and catabolic enzyme levels between the obstructive sleep apnea syndrome(OSA)patients and the control subjects.Methods Patients with OSA confirmed by PSG in our Sleep Center were randomly recruited from July to December,2009.Peripheral blood was obtained to isolate mononuclear cells and the mRNA levels of anandamide(AEA)synthase N-acylphosphatidylethanolamine hydrolyzing phospholipase D (NAPE),fatty acid amide hydmlase(FAAH)and 2-arachidonoylg lycerol(2-AG)synthase diacylglycerol lipase(DAGL)and hydrolase monoacyiglycerol lipase(MAGL)were measured by real-time polymerase chain reaction.The association between the severity of OSA and the enzyme levels were explored.Results There Was a significant difference in beth the NAPE and MAGL levels between patients with OSA and the control subiects.The level of MAGL Was related to some indices of severity of OSA,including the longest apnea time,lowest blood oxygen saturation and the micro-arousal index(r=0.31,0.24,0.34,respectively.all P＜0.05).Compared with patients with OSA alone,patients with OSA complicated by hypertension showed a different level of FAAH(P＜0.05).Conclusion OSA altered the expression of the ECS synthetic and catabolic enzymes,leading to an increase in endogenous cannabinoid substances.