Abstract Background: Gastrointestinal (GI) dysfunction is a danger for critically sick patients who receive mechanical breathing. During the course of enteral feeding in the early stages of critical illness, gastric residual volume (GRV) is used as a surrogate metric for GI dysfunction. This study aimed to investigate the effect of high gastric residual volume on critically ill patient outcomes. Design: A prospective, observational research design. Methods: A purposive sample of 60 adult critically ill patients of both sex from the intensive care units )sUCI( at Assiut University Hospital, Egypt were included in the study from August 2020 to April 2021. According to the measurement of gastric residual volume, those patients were not randomly allocated in group 1[the normal limit of gastric residual volume (NGRV) <500] and group 2 [High gastric residual volume (HGRV) >500]. Five tools were used to collect data included patient's assessment tool, APACHE 11 score, nutritional intervention assessment tool, gastric residual volume assessment tool, and Patient outcomes assessment tools. Results: there was a significant decrease in the Length of ICU stay, duration of mechanical ventilation, and mortality rate in NGRV group than the HGRV group (11.04±4.12 versus 13.91±5.88, 8.43± 4.5 versus 13.02 ±5.04, 30.4% versus 70.3%) respectively. Conclusion: HGRV had an adverse effect on critically ill patients' outcomes such as high ICU mortality, long duration of mechanical ventilation and long ICU stay. Recommendation: Frequent monitoring of gastric residual volume and gastric residual volume protocol and guidelines should be applied in ICU