Cerium conversion films were deposited on the surface of in situ aluminum-based composite in solutions containing different cerium chloride (CeCl3) and hydrogen peroxide (H2O2) concentrations at 30 °C. The morphology and composition of conversion films deposited in various solutions were investigated using scanning electron microscopy, energy dispersive x-ray analysis, and x-ray photoelectron spectroscopy (XPS). SEM observations revealed that only patches of film can be deposited on the composite surface when immersed in solutions with low CeCl3 and H2O2 concentrations. However, entire composite surface was covered with a compact film when immersed in a solution containing 10 g/L CeCl3 and 100 mL/L H2O2. XPS results indicated that cerium was incorporated as Ce4+ species in the hydrated oxide film. The formation of such hydrated conversion film on the composite resulted in low anodic current density and more noble pitting potential when exposed to 3.5% NaCl solution.