The surfactant-free synthesis of a solid film of ceria was carried out at the air–water interface from an aqueous solution of Ce(NO3)3 and gaseous NH3 as reactants. The synthesized CeO2−x·nH2O film consists of 2D nanocrystals with a fluorite structure. The film can form a planar coating on the surface of a solid substrate or transform into curved fragments upon drying, depending on the synthesis conditions.