Abstract: This research presents an eco-friendly biotechnological approach for synthesizing Zinc Oxide (ZnO) nanoparticles using orange peel extract (Citrus sinensis) as a natural reducing and stabilizing agent. Traditional synthesis methods often require toxic reagents and high energy; however, this study utilizes agricultural waste rich in polyphenols, flavonoids, and ascorbic acid to facilitate a sustainable "Green Chemistry" alternative.The experimental process involves reacting a zinc nitrate precursor with the aqueous extract under thermal stirring. Phytochemical functional groups reduce Zn^{2+} ions into intermediates, which are converted into stable ZnO nanoparticles through calcination (400°C–600°C), resulting in a pure hexagonal wurtzite structure.A primary focus is characterization via UV-Visible Spectroscopy. Successful synthesis is confirmed by a sharp Surface Plasmon Resonance (SPR) peak between 360 nm and 380 nm. This blue-shifted absorption indicates significant quantum confinement effects. Using the Tauc relation, the optical band gap was determined to be approximately 3.3 eV, confirming the high purity and semiconducting nature of the biogenic nanoparticles.Functional testing revealed exceptional antibacterial efficacy against S. aureus and E. coli. The mechanism involves the generation of Reactive Oxygen Species (ROS), which induce oxidative stress and physically disrupt bacterial cell membranes. This study confirms that orange peel-mediated synthesis is a cost-effective, non-toxic, and scalable route for producing high-quality ZnO nanoparticles. These findings suggest strong potential for applications in biomedical engineering, wastewater remediation, and antimicrobial coatings, offering a superior alternative to conventional synthetic methodologies.