Iron oxide nanoparticles (IONPs) have gained considerable attention due to their unique physicochemical properties especially in the environmental remediation practices. In the present study, IONPs were successfully synthesized using aqueous leaf extract of Plantago major as a simple and ecofriendly method to evaluate their efficient applicability as a dye removing nanomaterial. IONPs were characterized by transmission electron microscopy (TEM), particle size analysis (PSA), Fourier transform infrared (FT-IR) spectroscopy, X-ray diffractometer, vibrating sample magnetometer (VSM), and thermogravimetric analysis (TGA). Synthesized nanoparticles were spherical in shape with diameters in the range of 4.6–30.6 nm. The methyl orange (MO) removal ability of green synthesized IONPs was studied. The MO concentration is conveniently monitored using ultraviolet-visible (UV-Vis) spectroscopy during treatment with iron-catalyzed H₂O₂. The results showed dye removal ability with 83.33% efficiency in a 6-h process in solution containing the IONPs with H₂O₂.