Abstract: Abstract Objective: To explore the prediction value of the change in pleural pressure on the success rate of pleurodesis.Methods: The research is single centre and open experimental designed.We selected patients with malignant pleural effusion.Under ultrasonographic guidance, an appropriate intercostal space was selected.Then the patients were conducted the thin tube d?rainage in the pleural cavity. The pleural pressure, defined as the mean pleural pressure, was measured immediately and after 1000mL of effusion was withdrawn. Measurements were done while patients were in a sitting position. The elastance of the pleural space was calculated as the change in pleural pressure (in cm H2O) divided by the amount of fluid removed.After the effusion was completely drained off,the chest CT and HRCT on the lesion was undergone to confirm the degree and range of the involved lungs,visceral and parietal pleura. Cisplatin was instilled into the pleural cavity.After clamping the tube for 4 hours,the pleural space was drained consecutively.The tube was removed when less than 20ml of effusion was drained per day for 3 consecutive days and no effusion or only little amount of fluid was shown on the ultrasound.The intervention was scored as “successful”if no fluid reaccumulation was noted at 4 weeks, otherwise,scored as “failure”. Result:The study contained 72 patients with malignant pleural effusion.The outcome of 54 patients was successful,the other 18 patients was failure. Pleural elastance of the “successful” patients was less then the “failure”(P<0.05).All of the patients whose pleural elastance was ≥15cmH2O/L have “failure” outcome.The success rate of pleurodesis was 86.10% on the patients whose pleural elastance was <15cmH2O/L.There was no statistically difference on the success rate of pleurodesis between no obvious changes and the significant changes on images(P>0.05).Conclusion:There was good predictive value of the pleural elastance on the success rate of pleurodesis.