Abstract: Objective To investigate the clinical effect of using zerobalanced ultrafiltration on postoperative lung function of coronary artery bypass grafting (CABG) patients under cardiopulmonary bypass (CPB). Methods Forty coronary artery bypass grafting patients in the First Affiliated Hospital of China Medical University from June 2006 to December 2008 were enrolled in this study, and were divided into two groups based on different ultrafiltration procedures. Patients in the experimental group (n=20), 14 males and 6 females, with an age of 65.43±8.31 years, underwent zerobalanced ultrafiltration and conventional ultrafiltration after CPB was carried out. Patients in the control group (n=20), 15 males and 5 females, with an age of 66.51±7.62 years, only underwent conventional ultrafiltration after temperature restoration. Preoperative pulmonary function and arterial blood gas were tested routinely. Airway resistance (Raw), oxygenation index (OI) and alveolar arterial oxygen difference ［P(Aa)O2］ were measured at the following points: before CPB, at the end of CPB, 6 hours, and 12 hours after operation. Postoperative mechanical ventilation time was also recorded. Results There was no significantly statistical difference between the two groups of patients in pulmonary function and arterial blood gas indexes before operation, and Raw, OI and P(Aa)O2 before CPB (Pgt;0.05). Nevertheless, at the points of 6 hours and 12 hours after operation, Raw ［2.22±0.31 cm H2O/(L·s) vs. 2.94±0.42 cm H2O/(L·s), F=0.061, Plt;0.05; 1.89±0.51 cm H2O/(L·s) vs. 2.52±0.29 cm H2O/(L·s), F=0.096, Plt;0.05］ and P(Aa)O2 (86.74±7.63 mm Hg vs. 111.66±7.49 mm Hg, F=0.036, Plt;0.05; 74.82±5.67 mm Hg vs. 95.23±6.78 mm Hg, F=0.059, Plt;0.05) of patients in the experimental group were significantly lower than those of patients in the control group. At the same points, OI of patients in the experimental group was significantly higher than that of patients in the control group (384.33±30.67 vs. 324.63±31.22, F=0.033, Plt;0.05; 342.24±23.43 vs. 293.67±25.44, F=0.047, Plt;005). Ventilator support time of the experimental group was shorter than the control group (15.44±3.93 h vs. 20.68±5.77 h,Plt;0.05). Conclusion Zerobalanced ultrafiltration can improve pulmonary function after coronary artery bypass grafting and shorten postoperative mechanical ventilation time.