The microstructural evolution of coarse-grained Ni-48Al alloy during superplastic deformation at 1075 oC with initial strain rate of 1.5×10-3 s-1 was studied using EBSD (electron back-scattered diffraction) technique. The results show that before deformation, high angle grain boundaries dominate in the coarse-grained Ni-48Al alloy with few low angle grain boundaries. During the superplastic deformation, low angle grain boundaries with misorientations less than 5° occur successively. With the increase of the deformation, the misorientations of the newly-formed low angle grain boundaries increase, low angle grain boundaries with misorientations between 6o-15° are formed, and finally high angle grain boundaries with misorientations larger than 15° are formed. There exists a sort of dynamic equilibrium between the formation rate of low-angle grain boundaries and the rate of changing into higher-angle grain boundaries. The transformation from low angle grain boundaries to high angle grain boundaries makes the number of high-angle grain boundaries increase continuously and finally the grains are refined markedly.