Electromagnetic centrifugal casting technique based on magnetohydrodynamic principles has been applied to improve the solidification structure and mechanical properties of a 25Cr-20Ni-Fe-C alloy. The experimental results show that the solidification structure can be controlled by electromagnetic centrifugal casting. As the magnetic flux density increases, the solidification macrostructure changes from coarse columnar grains to a mixed structure consisting of fine curved columnar and equiaxed grains, and finally, into fine equiaxed grains. The columnar-equiaxed transition is achieved through the fracture of growing dendrites, and the size of equiaxed grains is also affected by the magnetic flux density. The alloy with equiaxed grain structure produced by electromagnetic centrifugal casting shows both better tensile strength at room and higher temperatures, and longer stress-rupture life compared with the same alloy with columnar grain structure produced by conventional centrifugal casting under the same stress.