Severe COPD exacerbations necessitating mechanical ventilation representing major aspect of disease management. Most weaning investigators have tried to find better weaning parameters which may correctly predict the outcome of weaning from mechanical ventilation in those patients. Objective To study the accuracy of the determinants of the respiratory muscle to predict weaning outcome Patients and Methods One hundred and two COPD patients necessitating mechanical ventilation >24 h underwent daily screen of subjective and objective indices for weaning readiness, and patients were classified into Group A (simple weaning group) (60 patients) and Group II (Prolonged weaning group) (42 patients). We assessed respiratory muscle determinants including: negative inspiratory force (NIF), occlusion pressure(P 0.1), and P 0.1/NIF. Also, rapid shallow breathing index (RSBI) was assessed.