This study reports the green synthesis of iron oxide nanoparticles (FeONPs) using Picralima nitida stem bark extract, a plant renowned for its rich phytochemical profile. The extract served as a natural reducing and stabilizing agent, leveraging bioactive compounds such as flavonoids, alkaloids, phenolics, saponins, and tannins to mediate nanoparticle formation. The synthesized FeONPs were characterized using UV–Vis spectroscopy, FTIR, dynamic light scattering (DLS), scanning electron microscopy (SEM), and X-ray diffraction (XRD), confirming the formation of crystalline, pyramidal nanoparticles with an average size of 45.15 nm. Antioxidant activity was assessed using the DPPH radical scavenging assay, with the FeONPs showing moderate activity (IC₅₀ = 1200.87 μg/mL) compared to the P. nitida extract (IC₅₀ = 14.93 μg/mL) and ascorbic acid (IC₅₀ = 420.55 μg/mL). These findings highlight the potential of P. nitida in green nanotechnology and suggest promising applications of FeONPs in biomedical and environmental fields due to their eco-friendly synthesis and inherent antioxidant properties.