The scanning electron microscope (SEM) observation and powder X-ray diffraction (XRD) measurements were performed for Bi-20at.%Mn alloys prepared by solid-phase reactive sintering in magnetic fields up to 15 T. The ferromagnetic MnBi grains were elongated and aligned along the magnetic field direction in the Bi-rich matrix for 523 K under μ0H ≥10 T. At 513 K, MnBi phase was not formed even the application of μ0H = 15 T. The obtained results suggested that the elongated grain of ferromagnetic MnBi was synthesized without connecting or rotating in magnetic field.