Abstract: 50 cases with cancerous pleural effusion were reported.This disease was commonly seen over 40 years old.They had progressive chest pain and dyspnea.The effusion was bloody,in large amount and in rapid increament,but they no obivous toxic symptoms.They originated frequently from lung cancer.Adenocarcinoma was commonest of all.Our data showed that level of LDH and CEA in the pleural fluid was helpful to distinguish between cancerous and tuberculosis pleural effusion.Measuring the level of CEA,LDH and ferritin was more important,while measuring the level of ferritin had no important value.