BACKGROUND: Hypoxemia during one lung ventilation (OLV) may occur in spite of high inspired oxygen concentration. The purpose of this study was to evaluate the effect of highfrequency jet ventilation (HFJV) alone to the non-ventilated lung or in combination with 5 cmH2O of positive end expiratory pressure (PEEP) to the ventilated lung on arterial oxygenation (PaO2) during OLV for thoracic surgery. METHODS: After endotracheal intubation with double lumen tube, arterial blood gases were measured 20 minutes after stabilization had occurred following onset of OLV, HFJV, and HFJV with 5 cmH2O of PEEP. RESULT: The mean PaO2 during OLV was 257.5+/-81.7 mmHg, and application of HFJV alone or with PEEP resulted in a significant increase in PaO2 to 356.6+/-79.1 mmHg and 354.9+/-66.6 mmHg, respectively (p<0.001). Alveolar-arterial oxygen differences were significantly decreased as compared to OLV. CONCLUSION: Both HFJV alone or in combination with 5cmH2O of PEEP are effective to improve oxygenation during OLV.