Background: Alterations in the methylation levels of tumor suppressor genes are considered as one of the essential aspects of malignancies. The present study explored the association of O6-methylguanine- DNA methyltransferase (MGMT) gene promoter methylation, as a tumor suppressor, with some organochlorine pesticides (OCPs) in primary brain tumor (PBT) patients. Methods: The present study was conducted on a total of 73 PBT patients. The patients’ serum was analyzed using gas chromatography for seven OCP derivatives. The methylation-specific PCR (MSP) method was also used to determine the methylation status of the MGMT promoter. Results: The current findings demonstrated that the methylation of MGMT promoter occurred in 22 out of 34 glioma cases (64%), but in only one out of 35 meningioma cases. No MGMT promoter methylation was observed in other PBT, hemangioma, and anaplastic medulloblastoma stages. Besides, there were significant associations between MGMT methylation and γ-HCH (odds ratio [OR]: 1.50; 95% CI: 1.03- 2.40, P= 0.04), 4,4DDE (OR: 1.44; 95% CI: 1.01- 2.05, P= 0.02), 2,4 DDT (OR: 1.23; CI: 1.04- 1.45, P= 0.03), and 4,4DDT (OR: 1.46; CI: 1.23- 2.15, P= 0.02) in glioma patients. Conclusion: The results of the study suggested that the hypermethylation of the MGMT promoter in glioma patients is associated with increased OCPs in their serum, especially γ- HCH, 4,4DDE, 2,4DDT, and 4,4DDT. Moreover, it may lead to the hypermethylation of the MGMT promoter gene. Hence, it can be concluded that exposure to OCPs may potentially induce glioma.