Objective To explore the efficiency,safety and suitable dosage of the non-invasive treatment of malignant gliomas with high intensity focused ultrasound(HIFU).Methods An extracorporeal HIFU with 9.7 MHz transducer(focal length: 4.5 mm,focal intensity: 2 500 W/cm~(2)) was used.Fifteen resected human malignant gliomas were randomly assigned to receive HIFU ablation for 10,20,30 s.After the treatment,the exposure coverage and marginal zone were collected and examined by HE staining and electron microscope.Results Exposure coverage and margin was safe in 10 s group.Typical coagulation necrosis was detected at exposure coverage with no detectable change at margin in 20 s group.Typical coagulation necrosis was seen at both exposure coverage and margin in 30 s group.Conclusion Under the parameters used in this study,20 s is a beneficial therapeutic dosage.HIFU is an accurate method for malignant gliomas ablation.