Thin films of CeO2 were prepared by a photochemical method using thin amorphous films of cerium(III) 2-ethylhexanoate as the precursor. The process was found to result from an initial photochemical extrusion of CO2 from the carboxylate ligand. This reaction led to the production of Ce(lI) complexes that were thermally unstable and to the production of the 3-heptyl radical. The photoefficiency of the reaction was 1.4, indicating that a radical chain reaction followed the initial photochemical process. Further evidence for a radical chain component arises from independent initiation of the reaction thermally with a free radical initiator. The final result of the reaction was the formation of an amorphous film that was analyzed as CeO2.0+/-0.3. The annealing of these films led to the formation of polycrystalline CeO2.