In order to investigate the modulation of the surface oxide layer on the surface plasmon resonance (SPR) properties of the metal thin films, Al metallic films are deposited with different thicknesses by DC magnetron sputtering by controlling the deposition power and deposition time. The as-deposited films are annealed to fabricate Al/Al₂O₃ composite films by regulating the annealing time and temperature. The structures, morphology and SPR properties of the Al/Al₂O₃ composite films are investigated by X-ray diffraction (XRD), atomic force microscope (AFM), spectro photometer and Raman spectroscopy, respectively. XRD results show that the phases of Al/Al₂O₃ composite films vary from amorphous to polycrystalline with a preferential orientation with the thickness increasing. Optical absorption spectra show that two peaks which correspond to the SPR absorption peak near 220 nm and the intrinsic absorption peak metal aluminum film near 830 nm. Raman spectrum reveals that the surface enhanced Raman scattering (SERS) intensity of Rhodamine B increases with the increasing thickness up to 14.5 nm and then decreases with the thickness further increasing. The results demonstrate that Al₂O₃ film has the capability to modulate the SPR with good properties.