Abstract: The crystallographic and magnetic structures of Er 2Fe 15 Mn 2C have been refined by Rietveld analysis of neutron diffraction data at room temperature. The refined results indicate that Er 2Fe 15 Mn 2C alloy has Th 2Ni 17 type (space group:P6 3/mmc) hexagonal structure, and the occupancy factors of manganese atoms are 0.039, 0.168, 0.022 and 0.336 at the 12 k, 12j, 6g and 4 f positions, respectively. The moments lie in the plane perpendicular to the six fold axis and exhibit planar magnetic anisotropy in Er 2Fe 15 Mn 2C. The value of Curie temperature T C is 349 K. The relation between magnetic properties and structures is discussed.