The Isumi Line (いすみ線, Isumi-sen) is a railway line in Chiba Prefecture, Japan, operated by the third-sector railway operating company Isumi Railway Company. It extends through the central eastern section of the Bōsō Peninsula, linking Ōhara Station in the city of Isumi, where it connects with the Sotobō Line, to Kazusa-Nakano Station in the town of Ōtaki, where it connects with the Kominato Line.