BACKGROUND: Among the many complications caused by obesity, the most common respiratory complication is upper respiratory obstruction during sleep caused by snoring. Long term snoring may lead to obstructive sleep apnea (OSA). The purpose of this research is to study the effects of non-surgical weight reduction on daytime sleepiness, fatigue, arterial stiffness, oxidative stress and antioxidant capacity of patients with OSA. METHODS: Twenty-one adults who were diagnosed with OSA by the ENT department were enrolled. They underwent a 12-week non-surgical weight reduction program based on diet and exercise. The patients were also treated with either Orlistat (Xenical(R)) or Sibutramine (Reductil(R)), when it was necessary. The effects of this treatment on daytime sleepiness and fatigue were measured by ESS (Epworth Sleepiness Scale) and FSS (Fatigue Severity Scale) respectively. Arterial stiffness, oxidative stress and antioxidant capacity were also measured and analyzed. RESULTS: The patients lost 1 kg to 12.9 kg (from 1.5% to 14.2% of basal body weights) of weight after the 12-week non-surgical weight reduction program. ESS were significantly decreased from 9.42 +/- 3.78 to 5.67 +/- 3.77 (P = 0.001) and FSS were decreased from 3.42 +/- 1.59 to 2.52 +/- 1.10 (P = 0.041) after the treatment. There were no significant changes on oxidative stress, antioxidant capacity and arterial stiffness. CONCLUSION: Daytime sleepiness and fatigue of patients with OSA were improved after the 12-week non-surgical weight reduction. Further research, of a larger scale, on the effects of non surgical weight reduction on oxidative stress, antioxidant capacity and arterial stiffness for patients with OSA is needed.