Introduction: Malnutrition is prevalent in intensive care unit patients and is associated with increased morbidity and mortality. Early administration of enteral nutrition to critically ill patients has been associated with a reduced length of hospital stay, enteral nutrition often is complicated by intolerance, as indicated by elevated volumes of gastric residuals. Aim of this study: Was to investigate the effect of implementing gastric residual protocol on critically ill patient outcomes. Design: A quasi- experimental research design was adopted to conduct this study. Setting: The general, trauma and anesthesia intensive care unit at Assiut university hospital. Subjects: A simple random sample of 68 adult critically ill patients who are mechanically ventilated and receiving enteral feeding assigned into two groups (35 patient in control group and 33 patient in intervention group). Results: There was a significant decrease in total amount of GRV, Length of ICU stay, mechanical ventilation duration, and mortality in the intervention groups than control groups, there was significant increase in delivered feeding amount, total calories in intervention groups than control groups p-value <0.05 Conclusion: Implementing gastric residual volume protocol had a positive effect on critically ill patient outcomes. Recommendation: Instruct health team in intensive care unit about gastric residual measurement, and management of high GRV.