AIM: To investigate the effects of 7.5% hypertonic saline on positive fluid balance and negative fluid balance, after radical surgery for gastrointestinal carcinoma.METHOIDS: Fifty-two patients with gastrointestinal carcinoma undergoing radical surgery were studied. The patients were assigned to receive either Ringer lactate solution following 4 mL/kg of 7.5% hypertonic saline (the experimental group, n = 26) or Ringer lactate solution (the control group, n = 26) during the early postoperative period in SICU. Fluid infusion volumes, urine outputs, fluid balance, body weight change, PaO2/FiO2 ratio, anal exhaust time as well as the incidence of complication and mortality were compared between the two groups.RESULTS: Urine outputs on the operative day and the first postoperative day in experimental group were significantly more than in control group (P＜0.000001,P= 0.000114). Fluid infusion volumes on the operative day and the first postoperative day were significantly less in experimental group than in control group (P = 0.000042,P= 0.000415). The volumes of the positive fluid balance on the operative day and during the first 48 h after surgery, in experimental group, were significantly less than in control group (P＜0.000001). Body weight gain post-surgery was significantly lower in experimental group than in control group (P＜0.000001). The body weight fall in experimental group occurred earlier than in control group (P＜0.000001). PaO2/FiO2 ratio after surgery was higher in experimental group than in control group (P = 0.000111). The postoperative anal exhaust time in experimental group was earlier than in control group (P = 0.000006). The overall incidence of complications and the incidence of pulmonary infection were lower in experimental group than in control group (P = 0.0175, P = 0.0374).CONCLUSION: 7.5% hypertonic saline has an intense diuretic effect and causes mobilization of the retained fluid, which could reduce fluid infusion volumes and positive fluid balance after radical surgery for gastrointestinal carcinoma, as well as, accelerate the early appearance of negative fluid balance after the surgery, improve the oxygen diffusing capacity of the patients alveoli, and lower the overall incidence of complications and pulmonary infection after the surgery.