Background: Diaphragmatic muscle dysfunction is common among the mechanically ventilated COPD patients which leads to weaning failure. Bedsides Diaphragmatic US can be used to predict the extubation outcome. Aim: To study the value of chest Ultrasonography in assessment of both diaphragmatic excursion and thickness as a weaning parameter in mechanically ventilated COPD patients. Patients and methods: The study was conducted on 48 mechanically ventilated COPD patients at time of weaning in the respiratory ICU, Zagazig University Hospitals. The following were done: ABG, chest X ray. Ultrasonographic assessment of the right diaphragm (thickness and excursion) during SBT. The results: Patients were classified according to weaning outcome into two groups: Successful Weaning group (35 patients) and Failed Weaning group (13 patients). Diaphragmatic excursion, tdi at end inspiration , tdi at end expiration , tdi % , tdi % /f , tdi % x Vt are significantly higher in the successful group (p < 0.001).Diaphragmatic excursion and tdi at end inspiration are considered an excellent significant discriminator for success of weaning (P