Abstract Background: Acid-base disorders are very common in critically ill as well as contribute significantly to morbidity and mortality. Aim: To evaluate the effect of acid-base disorders on mortality and level of consciousness for patients admitted to ICU. Design: descriptive exploratory research design was utilized to conduct this study .Setting: This study was carried out in anesthesia intensive care units at Assiut university hospital. Sample: One hundred sixty adult male and female patients. Tools: Two tools were used in this study, the Critically Ill Patients Characteristics tool, and Acid-base parameters assessment tool. Result: more than one third of the patients (36.3%) had respiratory alkalosis and was the most common acid-base disorder observed on admission . Metabolic acidosis and respiratory acidosis was associated with higher mortality (36.4%), and (22.75). Length of ICU stay was significantly higher in non-survivors (10.23±6.91 versus 7.60±4.69, p= 0.007). Mortality was significantly higher in the GCS < 9 group with metabolic acidosis (37.5 % versus 33.3 %, p=0.033). Conclusion: Respiratory alkalosis was a common acidbase disorder. Acidemia whether due to metabolic or respiratory acidosis is associated with increased mortality in ICU patients. Low GCS low is associated with increased mortality especially in the patients with metabolic acidosis. Recommendation: Closely monitoring and early managment is important to correct acid-base imbalance to avoid poor patient outcomes.