Background and aims: The aim of this work was to study the effect of intravenous glutamine dipeptide on the oxidative state and outcome in enterally nourished critically ill patients as regards the improvement of nitrogen balance, improvement of Body Mass Index (BMI), changes in the level of total antioxidants (especially glutathione), serum albumin, WCBCs and C-reactive protein, duration of stay in ICU and prognosis and incidence and frequency of complications. Patients and Methods: This prospective study was carried on 60 critically ill patients who were admitted to ICU and they received their nutritional requirements from protein, fat and carbohydrates according to food composition table via enteral route for 7-10 days. Patients were divided into 2 groups (A and B) with 30 patients for each group. The patients of group (A) had received their daily caloric requirements via the enteral route with parenteral GD for 10 days. Whereas the patients in group B had received their daily caloric requirements via the enteral route of nutrition without GD supplementation for 10 days. All critically ill patients were fully examined and assessed by the standard methods of critical care assessment. Also, other measures were taken including complete history, physical examination, anthropometric measures and investigations. Results: Parenteral GD proved that it improves nitrogen balance, serum total protein, serum albumin, glycemic control and serum total antioxidant (as glutathione). There was less GIT complications with the patients received glutamine dipeptide. Conclusion: GD improved patient’s nutritional status as regard serum albumin, total protein, nitrogen balance, and improved the patient’s outcome as regard (oxidative state: serum total antioxidants),also it improved the patient’s immunological reaction (total leukocytic count, C-reactive protein), and glycemic control. This was in addition to less frequency of GIT complications among those patients who received parenteral GD through the days of study. While the body weight, Body Mass Index, mortality rate, length of hospital stays, and the APACHE II score didn’t be affected by parenteral GD.