The effects of oxygenation of differential independent lung ventilation using HFJV (High Frequency Jet Ventilation) and CPAP (Continuous Positive Airway Pressure) on PaO2 and Qs/Qt were studied during one lung anesthesia in 11 mongrel dogs in left semilateral position with pentobarbital anesthesia. The dogs were divided into two groups. In group A(N = 7), following the conventional two lung ventilation, one lung ventilation, HFJV, one lung ventilation, cpap 5 cmH2O, and CPAP 10 cmH20 were applied sequentially. In group B(N =4), following the conventional two lung ventilation the above applications were reversed. In group A PaO2 revealed a similar increase among a two lung ventilation, CPAP 5 cmH2O, CPAP 10 cmH2O and HFJV. Intrapulmonary shunt showed the similar decrease among two lung ventilation, HFJV and CPAP 10cmH2O, but CPAP 5 cmH2O was higher than CPAP 10cmH2O. Although there were no statistically significant differences in PaO2 and shunt among each step in group B, HFJV showed a greate increase in PaO2, and shunt than one lung ventilation, CPAP 5 cmH 20) 20, and CPAP 10 cmH2O. In conclusion, HFJV proved to be more effective than CPAP 5 cmH2O in increasing PaO2 and decreasing shunt in differential independent lung ventilation. Both CPAP and JFJV should be applied in the deflation phase of the nondependent lung to cause an effective increase in PaO2. HFFV proved to be more effective than CPAP in recruiting the small airway closure.