Obstructive sleep apnea syndrome (OSAS) is defined as intermittent complete or partial upper airway obstruction during sleep, causing mental and physical effects. Both the local and systemic inflammation observed in OSAS induce certain potent pro-inflammatory mediators, which may contribute to the development of cardiovascular consequences. The present study was designed to evaluate the plasma levels of TNF-α, which is one of the known pro-inflammatory cytokines, in patients with OSAS and to assess the effect of surgical treatment on the levels of TNF-α levels. Twenty seven patients diagnosed to have OSAS, 7 non-apneic patients with chronic tonsillitis (non-OSAS patients), and 4 healthy subjects were enrolled in this study. Blood samples were collected one week preoperatively and postoperatively, and the plasma TNF-α levels were measured using high-sensitivity ELISA. The plasma TNF-α levels in patients with OSAS were significantly elevated in comparison to normal healthy subjects. In contrast, there was no difference between the patients with non-OSAS and healthy subjects. Moreover, the surgical treatment to enlarge the upper airway in patients with OSAS significantly decreased the levels of TNF-α levels. Surgical treatment of patients with OSAS reduces the plasma TNF-α levels, thereby ameliorating the systemic inflammation and preventing the development of cardiovascular consequences.