Abstract: Objective :To study the relationship between hypermethylation of CpG islands in theP16 gene promoter and the malignant grading of brain glioma, to observe the proliferative activity oftumor cells, and to explore the clinical significance of the detection of methylation status in plasma. Methods :Methylation status of the CpG islands in the P16 promoter was detected by semi-nestedmethylation-specific PCR (MSP) with DNA extracted from brain tumor tissues and paired plasmasamples of 40 patients with different grades of glioma. SP Immunohistochemistry was used to analyzethe expression of P16 and Ki-67 proteins. Results :The positive rate of methylation was 42.5% (17/40)in brain glioma tissues, while it was 27.5%(11/40) in plasma specimens (χ² =1.978 0, P=0.159 6).Immunohistochemical analysis showed an absence of P16 protein in 29/40 (72.5%) brain gliomas, whilehypermethylation was found in 16/29 (55.2%) brain tissue samples, suggesting that there was a highlysignificant (P=0.008 5) correlation between hypermethylation of the gene and absence of P16 protein.Hypermethylation of CpG islands in the P16 promoter was significantly related to increased malignantgrade of brain glioma (Tissue: χ² =11.428 8, P=0.000 7; Plasma: χ²=8.943 9, P=0.002 8). The level ofKi-67 protein increased significantly(P<0.05) in methylated brain gliomas in contrast to those that wereunmethylated. Conclusion :P16 gene silencing caused by hypermethylation of CpG islands is a majormechanism involved in tumor cell proliferation and it leads to the occurrence of brain glioma. DNA hypermethylation status in plasma can be a useful indicator for diagnosis and treatment of brain glioma.