Abstract：[Objective] To observe the effect of partial liquid ventilation(PLV) during cardiopulmonary bypass on gas exchange and histopathological changes of lung．[Methods] After cardiopulmonary bypass(CPB) was established，eighteen piglets were assigned randomly into 3 groups. Group I (Control Group): Animals in control group received no treatment but conventional mechanical ventilation；Group II:5ml/kg OxygentTM was instilled into the trachea during CPB；Group III: 15ml/kg OxygentTM was instilled into the trachea during CPB. The changes of gas exchange and lung compliance were examined before CPB、5min 、0.5hr、1、1.5 and 2hrs after withdraw of CPB. Histological sections were taken from right downsides of lung and stained by H & E．[Results]The Pa02 significantly increased and alveolar—aterial oxygen gradient (AaD02) markedly decreased in low dose PLV group（group II） compare with control group（group I） and large dose group（groupIII）(P<O．05) at the time of 0.5hr、1hr、1.5hr and 2hr post-CPB. The histopathological lesions of lung were less severe in low dose PLV group（group II） compare with control group and large dose group（group III）.[Conclusions] Partial liquid ventilation during CPB with low dose OxygentTM can improve the oxygenation of lung and increase the Pa02 after CPB．