Biodiesel is produced by the transesterification of oil triglycerides with methanol or ethanol, in the presence of a homogeneous or heterogeneous catalyst. This study aims to report the results of the transesterification of sunflower oil with methanol to produce biodiesel using CaO nanoparticles supported on NaX zeolite as catalyst. The effect of the CaO nanoparticles concentration on the NaX zeolite surface was studied in the range of 5-25 wt %. The transesterification reaction was carried out at reflux temperature of methanol, atmospheric pressure, a reaction time of 6 h, and with a 6:1 molar ratio of methanol to sunflower oil. Catalyst characterization was carried out by X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. It was concluded that methyl esters content is highly influenced by basicity and that the best catalyst was the one holding 16 wt % CaO nanoparticles. The produced biodiesel was 93.5% methyl esters and was found to fulfill the specifications of European Norm UNE-EN 14214 regarding viscosity, flash point, and acid value.