An anisotropic polycrystalline magnet of a Mn‐Al‐C alloy with (BH) max=6 MG⋅Oe has been successfully produced by extrusion at about 700°C. During the study on this ternary alloy system, a ferromagnetic phase (τ‐phase) single crystal was obtained by annealing a high‐temperature phase (ε‐phase) single crystal containing lamellae of the compound Mn3AlC, under the action of a uniaxial compressive stress. The formation process of the τ‐phase single crystal was analyzed. The process can be explained by the ε (h.c.p.) →ε′ (orthorhomb.) →τ (f.c.t.) transformations with the following orientation relationships: (0001)ε ∥ (100)ε′ ∥ (111)τ and ([1̄100]ε ∥ [001]ε′ ∥ [1̄1̄2]τ. The ε′‐phase is new and has a B19‐type structure. The ε→ε′ transformation is a disorder‐order transformation and the ε′→τ is martensitic. These single crystal results may be extended to the directionalization process for polycrystalline magnets.