Background: Sepsis is the leading cause of ICU admission associated with multiple organ dysfunction, which is cause of death in ICU. SOFA score is used to predict mortality in septic patients. APACHE II score is the severity of disease classification taken during first 24 hrs after admission. Aims and objectives: Study Validity of APACHE II and SOFA score in predicting prognosis in Mechanically Ventilated Patients. Methods: This prospective and observational study was performed from Nov18 to Apr20, at UP including 250 patients admitted in respiratory ICU who fulfilled the inclusion and exclusion criteria. Results: Out of 250 patients recruited, (43%) IMV, (41%) NIV and (16%) of the patients showed NIV failure. Most common indication of mechanical ventilation was acute on chronic respiratory failure (74%).COPD was the commonest pre-existing lung disease (50.8%). 71% mortality was observed in Renal disease. The highest complication was sepsis with septic shock. Patients who were on ventilator >7 days had higher mortality. Higher mortality was observed in IMV (44.9%). Mean APACHE II and SOFA scores in non survivors was higher than survivors which indicate good predictor of mortality. Highest mortality of 80% and 86.4% with cut off APACHE II ≥30 and SOFA score ≥ 18 was seen. In survivors, higher APACHE II and SOFA score had prolong length of ICU stay. Conclusion: APACHE II and SOFA score are strong predictor of mortality and provides the prognostic information.