Objective:To investigate the change of the airway oxidative stress marker,8-isoprostane(8-isoPG),and its clinical significance for patients with obstructive sleep apnea hypopnea syndrome(OSAHS). Methods:40 OSAHS patients and 30 normal controls were recruited in the study. Exhaled breath condensate(EBC) and serum 8-isoPG were assayed by ELLSA. 20 OSAHS patients were assayed again after three months’ treatment. Results:①The concentrations of 8-isoPG in EBC were (13.08 ± 1.42)pg/ml before sleep vs (14.93±1.39)pg/ml after sleep in 40 OSAHS patients(P < 0.01),and (11.06±0.72)pg/ml before sleep vs (10.97±0.7)pg/ml after sleep in 30 normal controls (P > 0.05). The concentrations of 8-isoPG in EBC after sleep were significantly higher than those before sleep in 40 OSAHS patients (P < 0.01). ②The serum levels of 8-isoPG were significantly higher in 40 OSAHS patients (36.59 ±14.89) pg/ml than those in 30 normal controls (19.91±7.76) pg/ml (P < 0.01). ③The concentrations of 8-isoPG in EBC of OSAHS patients after sleep were positive correlated with serum 8-isoPG levels (r=0.685,P < 0.01). ④After three months’ treatment with either auto continuous positive airway pressure (Auto-CPAP)or uvulopalatopharyngoplasty(UPPP),there was a significant decrease in the concentrations of 8-isoPG in both EBC and serum of 20 OSAHS patients before sleep and after sleep(all P < 0.01). ⑤ The concentrations of 8-isoPG in EBC of OSAHS patients after sleep were positive correlated with AHI,neck and waist circumferences(r=0.65,0.43 and 0.34,all P < 0.05)and negative with PaO2 (r=-0.31,P < 0.05). Conclusion:These findings suggest that oxidative stress is characteristic of OSAHS patients. The levels of 8-isoPG in exhaled breath condensate depend on the severity of the OSAHS and may prove useful in monitoring of airway oxidative stress of OSAHS.