Objective It’s unclear that the appropriate caloric goal for the internal patients in intensive care unit（ICU）.We evaluated the effect of restriction of calories , as compared with standard enteral feeding, on 28-day mortality among internal medicine adults in ICU, at the same time provided the full recommended amount of protein in both groups. Methods We randomly assigned 183 critically medical ill adults to underfeeding (40% to 60% of calculated caloric requirements) or standard enteral feeding (70% to 100%) for up to 14 days,with maintaining a similar protein intake in both groups. The primary outcome was 28-day mortality. Results Baseline characteristics were similar in the two groups; 88.0% of the patients were receiving mechanical ventilation. During the intervention period, the underfeeding group received fewer mean calories than did the standard feeding group ［(819±289) kcal per day vs. (1280±436) kcal per day, P＜0.05］; ［(47±13)% vs. (73±21)% of caloric requirements, P＜0.05］. Protein intake was similar in the two groups ［(47±16)g per day and (48±22)g per day, P=0.29］. The 28-day mortality was similar: 19 of 92 patients (18.9%) in the underfeeding group and 18 of 91 patients (19.7%) in the standard-feeding group died ［relative risk(RR) with underfeeding,0.95; 95%CI 0.67 to 1.19; P=0.7］. No serious adverse events were reported; there were no significant differences between the to groups with respect to feeding intolerance, diarrhea, and infections acquired in the ICU, or ICU or hospital length of stay. Conclusion With enteral feeding to deliver a moderate amount of nonprotein calories to critically ill adults, underfeeding is not associated with higher mortality than standard feeding.