Background: Diaphragmatic dysfunction was reported in most of mechanically ventilated patients and is considered one of the contributing factors of difficult weaning. Several parameters such as respiratory rate (RR), Tidal volume (TV), and rapid shallow breathing index (RSBI), are used as predictors of liberation failure from mechanical ventilation. The aim of the study was to investigate diaphragmatic dysfunction as an index of failure of liberation from mechanical ventilation and compare it with other conventional predictors of failure of weaning. Methods: 56 patients on invasive mechanical ventilation, admitted to our respiratory intensive care unit from November 2021 to May 2023, were included. Bedside chest ultrasound was done 30 minutes after starting spontaneous breathing trial. We recorded chest ultrasound indices; diaphragmatic excursion (DE) at inspiration (DE-insp) and forced inspiration (DE-forced-insp) and diaphragmatic thickness at inspiration (Tdi-insp) and expiration (Tdi-exp) and diaphragmatic thickening fraction (DTF). We compared these indices with predictors of weaning as TV, RR, RSBI, PaO2, PaO2/FiO2 ratio, and Total leucocytic count (TLC). Results: liberation failure from mechanical ventilation was detected in thirty cases (53.57 %). Also, those who failed weaning had significantly lower PaO2, pH, TV and significantly higher RSBI, RR, and TLC. As regard chest Ultrasound findings, patients with weaning failure had significantly lower DTF, Tdi-insp, and Tdi-exp. The sensitivity, specificity, negative predictive value, and positive predictive value of the diaphragmatic indices were all recorded and shown in tables. Conclusion: diaphragmatic dysfunction is considered an obstacle to weaning. Ultrasound diaphragmatic thickness is a better predictor of weaning failure than diaphragmatic excursion.