It is known that the circular RNA (circRNA) molecule circRIMS is overexpressed in gastric cancer and plays an oncogenic role. However, its role in other cancers is unknown. In this study, we analyzed its role in endometrial cancer (EC). EC and paired non-tumor tissue samples were collected from a total of 63 EC patients and subjected to total RNA isolations and reverse transcription quantitative polymerase chain reaction (RT-qPCR) to analyze the differential expression of circRIMS and miR-505. Overexpression of circRIMS and miR-505 was reached in EC cells and their interaction was analyzed using RT-qPCRs. The role of circRIMS in regulating miR-505 methylation was analyzed by methylation-specific RT-qPCR. Bromodeoxyuridine (BrdU) assay was performed to analyze the roles of circRIMS and miR-505 in regulating cell proliferation. circRIMS was upregulated in EC, while miR-505 was downregulated in EC. circRIMS and miR-505 were inversely correlated across both EC and non-tumor tissues. In EC cells, circRIMS overexpression decreased miR-505 expression and increased miR-505 gene methylation. BrdU assay showed that circRIMS overexpression increased cell proliferation and reduced the inhibitory effects of miR-505 overexpression on cell proliferation. circRIMS may downregulate miR-505 through methylation to increase cell proliferation.