Abstract: The corrosion resistance behavior of rare earth metal(REM) conversion coating on aluminum based metal matrix composites(MMC) Al6061/SiC P was examined by electrochemical method. Both anodic and cathodic reactions of corrosion were reduced by the existing film. Thus the corrosion rate was decreased. The microstructure of the film was studied by scanning electron microscope(SEM): the film consists of groups of different sizes of spherical particles which grew gradually to cover the background of the Al based MMC. The X ray diffraction (XRD) analysis revealed the non crystalline of the film. The constituent of the film was studied by X ray photoelectron spectroscopy (XPS): the film consists of cerium dioxide and hydrated cerium oxide.