In this article, we report the formation of ordered porous nanocrystalline ceria CeO2 during oxidative thermolysis of cerium formate Ce(HCOO)3. Ordering of the reaction product occurs due to the presence of similar structural elements in the CeO2 and Ce(HCOO)3 crystalline lattices. It was shown that the morphology and the structure of the products of thermal decomposition of Ce(HCOO)3 are greatly influenced by the composition of the gaseous atmosphere, in which the decomposition takes place. During thermal decomposition of Ce(HCOO)3 in an atmosphere of argon, no ordering of the synthesized CeO2 nanocrystals is observed. It was concluded that the presence of oxygen in the gaseous atmosphere is crucial for obtaining ordered nanocrystalline CeO2 from the Ce(HCOO)3 precursor.