Background: Chronic pleural empyema (CPE) is the last phase of the triphasic process of pleural empyema development. Lung decortication is the corner stone in management of chronic empyema. This study aimed to objectively evaluate the efficacy of conventional decortication operation in chronic pleural empyema in adult patients. Also to prove that decortication of variable sizes of chronic empyema thoracis lesions is followed by improvement considering respiratory impairment. Methods: This prospective clinical study was conducted on 103 patients undergoing elective lung decortication operation for management of chronic empyema. All patients were subjected to the history taking, general examination, chest examination, computed tomography (CT), pulmonary function test and arterial blood gases. Postoperative evaluation was done in outpatient clinic 6 months post operatively including: Full clinical examination, investigations (acute phase reactants, CT chest, PFT and arterial blood gases. Results: Total leucocytic count, ESR 1st hour, ESR 2nd hour and CRP were significantly decreased in post than pre. FEV1 and FVC were significantly increased in post than pre (P <0.001). FEV1 / FVC Ratio was significantly decreased in post than pre (P <0.001). Transverse and antero-posterior diameters of affected hemithorax were significantly increased in post than pre (P <0.001, 0.019 respectively). Transverse and antero-posterior diameters of normal hemithorax were insignificantly different between post and pre. PaO2 and SpO2 were significantly increased in post than pre (P <0.001). PaCO2 was significantly decreased in post than pre (P <0.001). Conclusions: The improvement in the lung function, arterial blood gases, transverse and antero-posterior diameter of affected and normal hemithorax was proposed to have resulted from the decortication in chronic empyema thoracis. Decortication of variable sizes of chronic pleural empyema lesions is followed by objective improvement considering respiratory impairment.