Abstract: Objective To observe the curative effect of the treatment with that pseudomonas aeruginosa agent on cure malignant pleural effusion. Methods Sixty-four patients with malignant pleural effusion were divided into treatment and control group randomly.Pleural effusion were drainaged first among all of these patients.After drainaged as clearly as possible,patients in treatment group were injected pseudomonas aeruginosa 5~8 ml and dexamethason 5~10 mg into the cavity,while the others were injected DDP 60~80 mg as the same time,1~2 times per week,2~3 times continuously. Results Twenty-five out of 32 cases were effective in the treatment group (78.1%), with a higher Karnofsky score and light side-effect;seventeen out of 32 cases were effective in the control group (53.1%), with more serious side-effect than treatment group. Conclusion Pseudomonas aeruginosa can control malignant pleural effusion effectively,and improve the quality of life with lighter side-effect as well.