The present work aims to synthesize CeO2 nanoparticles using Azadirachta Indica leaf extract as a reducing agent and Cerium nitrate as precursor. The crystalline nature of the synthesized CeO2 nanostructure was characterized by X-ray diffraction (XRD) and grain size was observed at 7.61 nm. The FT-IR spectrum provides qualitative and quantitative information of functional groups present in the sample. The results of XRD study reveal the diffraction pattern and show crystalline in nature. The absorption band due to the stretching frequency of Ce–O below 410 cm−1 indicates the formation of CeO2 nanoparticles. The absorption peak at 298 nm corresponds to the fluorite cubic structure of CeO2 nanoparticles; moreover, smooth and clear UV spectrum confirms that the synthesized nanoparticles are pure without any impurities and structural defects. Smaller crystal sizes with a higher surface area lead to higher antibacterial activity. The antibacterial studies performed against a set of bacterial strains showed that Gram-positive (G+) bacterial were relatively more susceptible than Gram-negative (G-) bacteria.