Obstructive sleep apnea syndrome (OSAS) is a common disease, which occurs in 4% middle-aged men and 2% middle-aged women. The characteristic of OSA is recurrent collapse of upper airway during sleep, which results in intermittent hypoxia and sympathetic activation. Cardiovascular complications associated with OSA include artherosclerosis, hypertension, coronary artery disease and congestive heart failure. Several inflammatory mediators including C-reactive protein (CRP), oxidative stress, adhesion molecules, vascular endothelial growth factor and proinflammatory cytokines, were found to be elevated in OSA, which attribute the developments of cardiovascular diseases in OSA. Our data showed serum levels of TNF were higher in OSA patients than in control subjects. And serum levels of TNF were inversely correlated with the lowest pulse oxygen saturation. After one-month CPAP treatment, serum of TNF could significantly go down. This finding suggested TNF was a good biomarker in studying OSA associated cardiovascular complications.