The diaphragmatic rapid shallow breathing index (D-RSBI), which is the ratio between respiratory rate (RR) and the ultrasonographic evaluation of diaphragmatic displacement (DD), is a new and promising tool to predict weaning outcome. Its accuracy in predicting weaning failure, in ready-to-wean acute exacerbation COPD (AECOPD) patients, needs to be evaluated. A prospective observational study was carried out on ready-to-wean AECOPD patients. During a T-tube spontaneous breathing trial (SBT) evaluation of the right hemidiaphragm displacement (ie, DD), M-mode ultrasonography to calculate the D-RSBI, as well as the RSBI (RR/tidal volume [VT]) were carried out simultaneously. Outcome of the weaning trial was recorded. Receiver operating characteristic (ROC) curves were used to evaluate the diagnostic accuracy of D-RSBI and RSBI. A total of 50 AECOPD patients requiring mechanical ventilation for more than 48 h who were ready to perform a SBT were included. Of these, 37 (74%) were successfully liberated from mechanical ventilation. Among the 13 patients who failed the weaning trial, 8 (62%) failed the SBT and reconnected to the ventilator, 2 (15%) were reintubated within 48 h of extubation and 3 (23%) required NIV support within 48 h of extubation. The areas under the ROC curves for D-RSBI and RSBI were 0.97 (p<0.001) and 0.67 (p<0.06), respectively. D-RSBI (RR/DD) is superior to the traditional RSBI (RR/VT) in predicting weaning outcome in AECOPD patients.