This research introduces a novel green synthesis approachfor fabricating multifunctional lanthanum oxide nanoparticles(La2 O3 ), including undoped, Cd-doped (Cd-La2 O3 ), and Ag-coated (La 2 O3 -Ag) variants, using Cymbopogon citratus (lemon-grass) leaf extract as a natural reducing and stabilizing agent.The synthesized nanoparticles were systematically character-ized using advanced analytical techniques. UV–visible spec-troscopy (UV–vis) revealed bandgap energies of 4.35, 3.25, and3.75 eV for La 2 O3 , Cd-La2 O3 , and La2 O3 -Ag nanoparticles, respec-tively, enabling enhanced optical and photocatalytic properties.X-ray diffraction (XRD) confirmed their crystalline nature withan average crystallite size of 18–22 nm. Scanning electronmicroscopy (SEM) and high-resolution transmission electronmicroscopy (HRTEM) images showcased distinct rod and spher-ical shape structures ranging from 20–50 nm. Energy-dispersiveX-ray (EDAX) verified the high purity and elemental composition.The nanoparticles demonstrated exceptional photocatalytic effi-ciency, achieving 92.43% degradation of methylene blue underUV light and 89.68% conversion of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). Additionally, nanoparticles demonstratedremarkable antibacterial activity against the Gram-positive andGram-negative bacteria, outperforming ampicillin. The inhibitionzones exceeded 18 ± 2 mm by disc diffusion assay. Antioxidantassays revealed superior free radical scavenging (ROS) abilitycompared to ascorbic acid, reducing DPPH radicals by 70 ± 5%at 1000 μg/mL. Hemolytic analysis indicated minimal cytotoxic-ity at higher concentrations, underscoring their biocompatibility.This study highlights the novelty and multifunctionality of La2 O3nanoparticles, demonstrating their potential for advanced envi-ronmental remediation and biomedical applications.