Abstract Background: Patients receiving mechanical ventilation have an increased risk of complications resulting in excess morbidity and mortality. Aim of Study: This study aimed to identify the acute effect of chest physical therapy on arterial blood gases of mechanically ventilated patients. Material and Methods: Sixty mechanically ventilated patients participated in the study. Their age ranged from 40 to 60 years. The patients were assigned into one study group including both sexes who received a chest physiotherapy protocol in form of (manual hyperinflation, vibration, percus-sion, suctioning, upper and lower limbs exercise and ending position) for one session. Arterial Blood Gases (ABG) includ-ing (pH, PaO2, SO2, PaCO2 and HCO3) were assessed by arterial blood sample analysis through the Laboratory GEM premier 3000 device. All the assessment was done for every patient pre and post chest physiotherapy protocol. Results: The results revealed a marked improvement in arterial blood gas exchange as compared to base line reflected by a highly significant statistical increase in PaO2 and SaO2 (p < 0.001) and a significant decrease in PaCO2 (p < 0.001) while with no significant changes regarding pH and HCO3 (p=0.36 and 0.15 respectively). Conclusion: Chest physiotherapy protocol is an effective method for improving arterial blood gases of mechanical ventilated patients acutely.