The synthesis of iron oxide nanoparticles (FeONPs) by a recently developed green approach is very promising due to its non-toxic and environmentally friendly behavior. In this study, biosynthesis of FeONPs was prepared using leaf extract of plant with ferric chloride solution. They were characterized by UV-vis spectrum show a peak at 293 nm, confirming the presence of FeONPs. A Fourier-transform infrared (FTIR) analysis of FeONPs displays spectra that are identical to functional groups and X-ray diffraction (XRD) analysis demonstrated that the particles were of high purity with crystalline cubic structure phases in nature. The structural characteristics were determined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis which showed spherical morphology with particle diameters of between 43 nm. Energy dispersive x-ray spectroscopy (EDAX) confirmed the presence of Fe elements at 3 keV. The FeONPs showed strong antibacterial activity against Gram-positive pathogens with having the inhibition zone ranged from 19 ± 0.42 mm at a concentration of 75 μg/mL. Antioxidant activity observed more effective in assays for DPPH and ABTS radical scavenging. The anti-inflammatory activity had a stronger effect than the IC values for albumin denaturation (58.43 µg/mL) and human red blood cells (59.57 µg/mL). The FeONPs were an IC value of 48.51 μg/mL when used against breast cancer (MCF-7) cell lines. Further, according to the results of the photocatalytic activity of methylene blue (MB) dye breakdown in sunlight, MB decomposed by 85.83% after 70 min. Therefore, all of these results point to the possibility that produced FeONPs might be economical and safe for the environment when it comes to removing dyes and propose their effective applications in biologic domains in future.