In this study, we first performed sequencing to evaluate the detailed methylation patterns of two CpG islands in the promoter region of miR-509-3p in EOC cell lines and tumor samples and found that promoter hypermethylation by DNMT1 resulted in miR-509-3p silencing in ovarian cancer and that miR-509-3p hypermethylation was associated with a decreased survival time. The gene discussed is DNMT1; the disease is neoplasm.