The association of physicochemical properties of CeO2-NPs (CeO2 nanoparticles) per se with their transformation is not well understood. This study for the first time compared the translocation and transformation of octahedral, cubic, rod, and irregularly shaped CeO2-NPs in hydroponic cucumber plants. Cerium contents in roots were close between different treatments, while the largest amount (153 mg/kg) of Ce accumulated in rod-like CeO2-NP treatments. Transmission electron microscopy and X-ray absorption near edge spectroscopy show that rod CeO2-NPs transformed faster and more than other CeO2-NPs, with nearly 40% of Ce in the form of Ce(III) species in roots (CePO4) and shoots (Ce carboxylates). Rod-like CeO2-NPs transformed to a degree greater than those of the other CeO2-NPs in solution simulating the plant exudates, indicating that rod-like CeO2-NPs have the highest chemical reactivity. These results suggest that the intrinsically different chemical reactivity of differently shaped CeO2-NPs resulted in their different transformation and translocation capacities in plants. This study provides new insight into plant–NP interaction, highlighting the significance of the shape of nanoparticles in assessing their environmental behavior and impacts. We suggest that the influence of shape should be also considered for other nanomaterials and systems in developing an accurate understanding of the nano–bio interactions.