Objectives To investigate the effect of the combined treatment with probiotics and lactulose of gastrointestinal function and postoperative infection after open cardiac surgery. Methods We retrospectively analyzed the clinical data of 264 patients underwent cardiopulmonary bypass in our hospital between August 2013 and June 2014. There were 129 males and 135 females at the mean age of 53.06±10.97 years. We divided those patients into a treatment group and a control group. In the treatment group, there were 58 males and 63 females at the mean age of 52.29±14.31 years. They took probiotics and lactulose from the first day to the seventh day after operation. In the control group, there were 71 males and 72 females at the mean age of 52.29±14.31 years. They didn’t take probiotics or lactulose after the surgery. Procalcitonin (PCT) and lipopolysaccharides (LPS) concentrations were measured before operation, at 24 hours postoperatively, at 72 hours and on the seventh day. We recorded the condition of postoperative infection, gastrointestinal disorders and relative informations. Results The PCT and LPS concentrations in the treatment group after 72 hours postoperatively were statistically lower than those of the control group (1.04±5.39 ng/ml vs. 3.51±4.28 ng/ml, P=0.04; 11.28±4.34 EU/ml vs. 21.59±7.34 EU/ml, P=0.03). The PCT and LPS concentrations in the treatment group were also statistically lower than those of the control group on the 7th day postoperatively (0.17±2.79 ng/ml vs. 1.98±4.62 ng/ml，P=0.04; 6.74±6.38 EU/ml vs. 15.96±4.61 EU/ml, P=0.01). The ICU stay time (43.25±14.36 h vs. 63.47±24.46 h, P=0.01) and postoperative hospital stay time (15.07±4.52 d vs. 21.08±6.49 d, P=0.02) were significantly less in the treatment group than those in the control group. The morbidity of infection and the morbidity of gastrointestinal disorders of the treatment group were statistically less than those of the control group (1.65% vs. 5.59%, P=0.00; 2.48% vs. 6.99%, P<0.001), and there was no statistical difference in mortality between the two groups (1.65% vs. 2.10%, P=0.12). Conclusions The combined treatment with probiotics and lactulose can improve the postoperative inflammatory reaction, gastrointestinal function, and reduce the morbidity of infection.