The purpose of this research was to detect the effect of training of inspiratory muscle on respiratory failure patients. Method: Thirty patients with respiratory failure were selected from Cairo university hospital (critical care department). These patients were divided equally into two groups, study Group A and control Group B. Each patient of Group A received inspiratory muscles training using threshold inspiratory muscle trainer (IMT), while patients of Group B received only chest physiotherapy. Oxygen level and respiratory muscles strength for each group were measured. Result revealed significant improvement in both groups, improvement was higher in Group A more than Group B regarding oxygen level and respiratory muscles strength. Conclusion: Training of respiratory muscles using threshold inspiratory muscle trainer could be a useful in improving oxygen level and respiratory muscles power in patients with respiratory failure, this study revealed that, respiratory muscles training could be a helpful tool to improve oxygen level and inspiratory muscle strength for respiratory failure patients.