The production of biodiesel from waste cooking oil represents an alternative energy means of producing liquid fuels from biomass. On the other hand it reduces the harm full air pollutants and when waste cooking oil (WCO) is recycled, several gallons of waste oil can be diverted from landfills and municipal sewage pipes. A solid base nanocatalyst of calcium oxide is synthesized by thermal-decomposition method using calcium nitrate tetrahydrate (Ca(NO3)2.4H2O) as precursor, sodium hydroxide (NaOH) aqueous solution as a precipitant, and ethylene glycol as medium. The synthesized white crystal CaO is characterized by using X-Ray diffraction and Scanning Electron Microscope (SEM) techniques. The results showed that the mean size of nano-CaO is about 27.3 nm with a morphology of irregular shape and porous in structure. The results of these study indicates that the conversion of WCO to biodiesel using CaO as heterogeneous catalyst provided a maximum conversion of 96%, at optimized experimental conditions. The optimum yield was obtained when the oil to methanol molar ratio was 1:8, the reaction time was 90 minute, the temperature was 50 to 55 oC and the catalyst mass was 1% in relation to the oil mass used in the transesterification reaction. The Biodiesel viscosity, specific gravity, total acidity, ash content, sulfur content, water and sediment were according to the ASTM D6571 standard for biodiesel. The results of this study showed a high performance, hence the proposed simple and effective method of production could be used as an innovative way to produce biodiesel.