The crystallization of amorphous $alpha$-Fe$_2$O$_3$/$alpha$-AI$_2$O$_3$(0001) thin films during thermal annealing in air has been studied using real-time synchrotron x-ray scattering. The well aligned (0.02$^{circ}$/ FWHM) $alpha$-Fe$_2$O$_3$and Fe$_3$O$_4$interfacial crystallites (50- -thick) coexist on the $alpha$-AI$_2$O$_3$(0001) in the sputter-grown amorphous films at room temperature. The amorphous precursor is crystallized to the epitaxial $alpha$-Fe$_2$O$_3$grains in three steps with annealing temperature; i ) the growth of the well aligned $alpha$-Fe$_2$O$_3$interfacial crystallites, together with the transformation of the Fe$_3$O$_4$crystallites to the $alpha$-Fe$_2$O$_3$ crystallites, ii ) the growth of the less aligned (3.08$^{circ}$ FWHM)$alpha$-Fe$_2$O$_3$grains on the well aligned grains (＞40$0^{circ}C$), and iii) the nucleation of the other less aligned (1.39$^{circ}$ FWHM) $alpha$-Fe$_2$O$_3$grains directly on the $alpha$-AI$_2$O$_3$substrate (＞$600^{circ}C$). The effective thickness thinner than 230 may be very useful for enhancing the epitaxial quality of $alpha$-Fe$_2$O$_3$/AI$_2$O$_3$(0001) thin films.