Abstract: Natural morphology of (Mn,Fe)S single crystal in ZG25 cast steel have been discovered and investigation using SEM505 scanning electron microscope. The face-centred cubic (Mn,Fe)S single crystal at equilibrium state is shown to be tetrakaidecahedron consisted of eight 111 planes and six 100 planes, and is a typical example of the Oh-m3m cubic crystal system. Infact, this may be first report on tetrakaidecahedron morphology of the (Mn,Fe)S single crystal in ZG25 cast steel.