The colloidal and chemical stability of CeO2 nanoparticles used in a diesel additive (viz. Envirox[trade mark sign]) was studied at different stages of their lifecycle (formulation{,} use{,} end of life). After combustion at a temperature close to that of diesel engines{,} the size of the CeO2 crystallites increased significantly without detectable Ce(iii) in the structure and remaining organic compounds at the surface. Regardless of the aging conditions (salinity{,} light{,} pH){,} the dissolution kinetics of the combusted particles were slowed down compared to that of the initial CeO2 nanoparticles. After 2 days at 0.1 g L-1 of salts{,} no more than 0.01% of the total Ce was released from the 850 [degree]C-combusted Envirox[trade mark sign] versus 1.5% for the uncombusted Envirox[trade mark sign]. Both the crystal growth during combustion and the degradation of the organic matrix will govern the aggregation and dissolution kinetics/mechanisms once the CeO2 particles are released into the environment at different stages of their lifecycle. Such a study is a prerequisite needed before any assessment of the environmental risks of CeO2 nanoparticle-based diesel additives is performed.