Abstract: For the cold-rolled aluminum lubricated with water-based emulsion, two typical defects always can be found on the surface of the aluminum plate: One is the black stripe parallel to the rolling direction. Another is the erosion spot. In this paper, the two defects were investigated by several surface analysis techniques, i.e. surface topography, scanning electron microscopy, energy dispersive spectrometer, and X-ray photoelectron spectroscopy. In the area of the black stripe, there were many micro-cracks on the surface. The black strip defect was attributed to the enhanced oxidation in the area of micro cracks and the residual oil from the emulsion in the cracks which can hardly be removed. In the eroded area, thick oxide layer can be found on the surface, which was originated from the electrochemical reaction between the aluminum and the residual water on the surface.