<p>Knowing how metal oxide nanoparticles affect aromatic and medicinal plants is fundamental for optimizing nanofertilizer application. Rosemary lacks comprehensive studies evaluating how foliar-applied zinc oxide (ZnO) and iron oxide (Fe₂O₃) nanoparticles (NPs) modulate antioxidant enzymes, mineral accumulation, and cellular ultrastructure. Therefore, this study investigated the effects of foliar sprays of ZnO-NPs and Fe₂O₃-NPs (25–100&#xa0;mg L⁻¹) on rosemary biochemical and physiological responses. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to characterize ZnO and Fe₂O₃ nanoparticles. Then, foliar applications of both nanoparticle suspensions were applied to rosemary seedlings, followed by biochemical assays, mineral analysis, and microscopic and ultrastructural examinations. TEM demonstrated the production of ultra-small ZnO and Fe₂O₃ nanoparticles, and XRD confirmed their purity, crystallinity, and nano-scale dimensions. Both kinds of nanoparticles significantly affected protein accumulation and altered antioxidant enzyme activities. For example, total soluble protein content increased markedly. Also, guaiacol peroxidase (GPOX), superoxide dismutase (SOD), polyphenol oxidase (PPO), and glutathione peroxidase (GP_X) enzymes were enhanced – particularly at 100&#xa0;mg L⁻¹ – while ascorbate peroxidase (APX) exhibited dose-dependent inhibition. Mineral analysis indicated increased accumulation of zinc (Zn), iron (Fe), and potassium (K), with solely potassium uptake showing a robust, dose-dependent correlation in the presence of ZnO-NPs. Additionally, TEM images showed enhanced cell wall thickening, cellular compaction, and the formation of electron-dense aggregates. Overall, the 100&#xa0;mg L⁻¹ foliar dose was the most effective causing clear biochemical and structural changes. These findings provide new insights into how rosemary responds to ZnO- and Fe₂O₃-based nanofertilizers.</p> Graphical Abstract <p></p>