This study focuses on the green synthesis of iron oxide (Fe2O3) nanoparticles using guava leaf extract as a reducing agent. The methodology involves the extraction of guava leaves to create an aqueous reagent solution, followed by the synthesis of Fe2O3 nanoparticles through a series of processes including centrifugation and annealing. The synthesis procedure involved mixing the guava extract with an iron nitrate solution, stirring, and allowing the formation of nanoparticles, which were subsequently annealed at 600°C. Characterization of the resulting nanoparticles was carried out using X-ray diffraction (XRD), revealing a rhombohedral structure with an average crystallite size of approximately 40-45 nm. Ultraviolet-visible (UV-Vis) spectroscopy indicated strong absorption in the 500-800 nm wavelength range, with the calculated optical bandgap of the synthesized nanoparticles being 2.08 eV. Transmission electron microscopy (TEM) analysis showed that the nanoparticles predominantly exhibited irregular, quasispherical shapes with a tendency for slight agglomeration. The findings demonstrate the efficacy of the green synthesis approach not only as a sustainable method for producing Fe2O3 nanoparticles but also highlight their potential applications in fields such as environmental remediation, biomedicine, and catalysis.