The aim of this study was to determine how cerium dioxide nanoparticles (CeO₂ NPs) affect the growth and physiology of Brassica napus plants. CeO₂ NPs were biosynthesized using Aloe Vera extract and characterized using a UV-visible spectrophotometer, X-ray diffraction, Fourier transform infrared spectroscopy, Zeta potential, and particle size (DLS) as well as transmission electron microscopy. Following foliar treatment with 250, 500, and 1000 ppm of CeO₂ NPs, the growth, and metabolism of Brassica napus were evaluated. Exposure to 500 ppm CeO₂ NPs significantly enhanced morphological characteristics, antioxidant enzymes, phenol content, tocopherol, and chlorophyll content as well as carotenoid levels in B. napus. Assessment of oxidative stress in B. napus leaves treated with 500 CeO₂NPs showed high levels of super oxide anion radical (o₂·¯) and hydrogen peroxide and low content of MDA, as well as inhibition in the activity of Lipoxygenase enzyme. Histochemical staining of B. napus leaves using nitro blue tetrazolium confirms the role of spraying of 500 ppm of CeO₂ NPs in the accumulation of oxidative molecules in leaves. Gene expression assay for SOD and MT highlighted the role of CeO₂ NPs in the regulation of stress-related genes in tested plants. The changes in ultrastructure of Brassica napus leaves treated or untreated with 500 ppm of CeO₂ NPs for two weeks were examined using a transmission electron microscope. (we highly appreciate this reviewers precise comment)