Iron oxide nanoparticles stabilized with Moringa arborea were synthesized. The study aimed to investigate the cytotoxic potential of IONPs through various assays, such as trypan blue and MTT assays, of the synthesized iron oxide nanoparticles (IONPs). The Moringa arborea-mediated IONPs (M A IONPs) were analyzed using a range of techniques, including Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), UV-vis spectroscopy (UV-vis), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The FTIR, XRD, and SEM-EDX results confirmed the successful synthesis of IONPs. A gas chromatography–mass spectrometry (GC-MS) analysis of the plant revealed various compounds of medicinal value. The analysis of the UV-vis spectra indicates an absorption peak at 314 nm, thereby ensuring both the successful synthesis and remarkable stability of the nanoparticles. The nanoparticles exhibited a uniform spherical morphology and contained Fe, O, N and some minor elements, confirming the formation of IONPs NPs. The cytotoxic potential on MCF-7 and MDA-MB 231 human breast cancer cells was observed with various concentrations of M A IONPs, and the cytotoxicity results revealed an IC₅₀ of 48.7 μg/mL and 54.6 μg/mL, respectively . Stable IONPs were synthesized using a methanolic extract of Moringa arborea. The nanoparticles exhibited cytotoxic potential on highly and weakly metastatic human breast cancer cell lines.