This paper reports the synthesis of platelike CeO2 nanoparticles by a simple, cost-effective, and environmentally friendly method using cerium(III) acetate hydrate and freshly extracted egg white (ovalbumin) in an aqueous medium. A platelike structure of CeO2 nanoparticles having the particle size of 6−30 nm was obtained by calcining the precursors in air at 400, 500, and 600 °C, for 2 h. Results from XRD, Raman spectroscopy, and SAED analysis indicated that the synthesized CeO2 nanoparticles have the fluorite structure of the bulk CeO2. All samples show a strong UV−vis absorption below 400 nm (3.10 eV) with a well-defined absorbance peak at around 284 nm (4.37 eV). The estimated direct band gaps are 3.61, 3.59, and 3.57 eV for the samples calcined at 400, 500, and 600 °C, respectively. These band gaps are 0.42, 0.40, and 0.38 eV higher than that of bulk CeO2, indicating the quantum confinement effect of the nanosize particles. The 400 and 500 °C calcined samples exhibited similar emission peaks of room-t...