Cerium oxide nanoparticles (CON) are gaining considerable interest as an attractive and essential catalytic material in the chemical process of environmental and energy industry. The synthesis of ultra-small CON remains challenging task for their industrial scale implementation. Herein, we report a novel and sustainable method for synthesizing CeO2 nanoparticles under direct sunlight with Tryptophan and Tyrosine as UV light active capping agents. Different properties of synthesized CON such as crystalline structures, morphology, phase, and size were examined by SEM, HR-TEM, XRD, Raman Spectroscopy and UV-Vis Spectroscopy. Further, XPS analysis was carried out for the determination of surface composition of CON synthesized under direct sunlight. CON synthesized using Tryptophan and Tyrosine shows higher Ce3+ species on the surface due to high UV absorption. Further, CON has showed excellent catalytic activity for the synthesis of dimethyl carbonate from transesterification of ethylene carbonate with methanol due to increased Ce3+ species. CON synthesized using tryptophan showed an excellent yield of 58.54% in the transesterification of ethylene carbonate at 140 degrees C in 3 h. [GRAPHICS] .