Mn-Bi alloy films were prepared by simultaneous vacuum deposition at liquid N 2 temperature and their structures were investigated by transmission electron microscopy and electron diffraction. Films with compositions in the range of 34 to 63 at% Mn have the Bi lattice structure at room temperature. Films with composition in the range of 68 to 95 at% Mn show diffuse haloes at room temperature. When they are heated above room temperature, those in the range of 70 to 85 at% Mn show nucleation and grain growth crystallization, whereas the films of 68 and 95 at% Mn show only grain growth crystallization. The films in the range of 70 to 85 at% Mn are concluded to be amorphous at low and at room temperature. Some of the crystals obtained by nucleation and the grain growth crystallization grow as large as 10 μm in length. Their diffraction patterns are not ascribable to reported crystals in this alloy system.