Abstract: Objective To assess the intestinal barrier function of patients with advanced digestive tract malignant tumors by measuring the changes in intestinal permeability. Methods Sitteen patients with digestive tract tumors and 16 healthy volunteers were enrolled. After oral administration of mannitol and lactulose in deionized water, the 6-hour urine samples were collected for analyzing mannitol and lactulose concentrations using gas-liquid chromatography. Results Urine lactulose concentration and lactulose/mannitol (L/M) ratio of the tumor patients were increased in comparison with those of the healthy subjects (P<0.05). Conclusion The intestinal permeability increased in these tumor patients, indicating intestinal barrier dysfunction.