AIM： To investigate whether illness severity has an impact on gastric residual volume （GRV） in medical critically ill patients. METHODS： Medical intensive care unit （ICU） patients requiring nasogastric feeding were enrolled. Sequential Organ Failure Assessment （SOFA） score was assessed immediately preceding the start of the study. Acute Physiology and Chronic Health Evaluation （APACHE） Ⅱ scores were recorded on the first, fourth, seventh, and fourteenth day of the study period. GRV was measured every 4 h during enteral feeding. The relationship be-tween mean daily GRV and SOFA scores and the correlation between mean daily GRV and mean APACHE Ⅱ score of all patients were evaluated and compared. RESULTS： Of the 61 patients, 43 patients were survivors and 18 patients were non-survivors. The mean daily GRV increased as SOFA scores increased （P 0.001, analysis of variance）. Mean APACHE Ⅱ scores of all patients correlated with mean daily GRV （P = 0.011, Pearson correlation） during the study period. Patients with decreasing GRV in the first 2 d had better survival than patients without decreasing GRV （P = 0.017, log rank test）. CONCLUSION： GRV is higher in more severely ill medical ICU patients. Patients with decreasing GRV had lower ICU mortality than patients without decreasing GRV.