We report on the synthesis of single-crystal and polycrystalline samples of Ce 3 − x Mg x Co 9 solid solution ( 0 ≤ x ≲ 1.4 ) and characterization of their structural and magnetic properties. The crystal structure remains rhombohedral in the whole composition range and Mg partially replaces Ce in the 6 c site of the CeCo 3 structure. Ferromagnetism is induced by Mg substitutions starting as low as x = 0.18 and reaching a Curie temperature as high as 450 K for x = 1.35 . Measurements on single crystals with x = 1.34 and T C = 440     K indicate an axial magnetic anisotropy with an anisotropy field of 6 T and a magnetization of 6     μ B / f . u . at 300 K. Coercicity is observed in the polycrystalline samples consistent with the observed axial magnetic anisotropy. Our discovery of ferromagnetism with large axial magnetic anisotropy induced by substituting a rare-earth element by Mg is a very promising result in the search of inexpensive permanent-magnet materials and suggests that other nonmagnetic phases, similar to CeCo 3 , may also conceal nearby ferromagnetic phases.