Abstract In this work, we presented our effort to understand the effect of the operating parameters of the microwave oven (power and irradiation time) on the structural and morphological changes in ceria (CeO 2) nanostructures. A series of controlled experiments were carried out to understand the crucial factors determining the formation of ceria nanostructures with spheres and rods like morphology. By adjusting the experimental parameters different ceria nanostructures such as spheres, cubes and rods were obtained. The variation of the lattice parameter and morphology of the prepared samples was discussed by structural studies. The W H analysis was implemented to calculate the average crystallite size and microstrain. The influence of morphology and microstrain on the band gap energy, luminescence and photocatalytic activity of the synthesized samples was discussed. The observed variation in the band gap was explained based on the variation of the crystallite size. Also, the observed variation in the ratio of the intensity of band gap related emission (I Bg) and defects related emission (I def) was discussed. In addition, the enhanced photocatalytic performance of the prepared ceria nanostructures with different morphology was discussed. Graphical abstract Hierarchical ceria nanostructures are prepared using the commercial microwave oven. The selection of operating parameters of the microwave oven (output work power and different irradiation cycles) resulted in the ceria nanostructures such as spheres, cubes and rods. The as-prepared nanostructures possessed morphology dependent photocatalytic activity. Image 1 Highlights • The crystallization of ceria nanostructures is ultrafast (≤2 min). • Commercial Microwave oven (power and irradiation time) variation induced changes in morphology. • Crystallite size dependent bandgap of ceria nanostructures. • Luminescence in the visible range due to the various F -centers (oxygen vacancies). • Microstrain and morphology influence on photocatalytic properties. • Relaxation of microstrain favored the enhanced photocatalytic activity. [ABSTRACT FROM AUTHOR]