A simple method has been developed in our laboratory, namely, lonization Loss Spectros-copy (ILS) for unoccupied DOS measurement which can be performed with existing Auger electron spectroscopy apparatus.The results of spin-orbit splitting and binding energy obtained by ILS are in excellent agreement with that of ESCA. The ILS spectra of 3d transition metals, Ti, Cr, Ni, Cu have been measured. The typical integral spectra exhibit a peak-like shape with different intensity and width which reflects the width of the unoccupied DOS. Since the unoccupied 3d DOS of Cu is zero, the ILS spectrum of Cu measured is shown by a step-like structure resulting from the flat, narrow 4s DOS.