This study investigates the utilization of crude oil waste fly ash (COFA), generated by electrical and desalination power plants in Saudi Arabia, to improve the performance of asphalt flexible pavements. Fly ash by-products from these plants were incorporated into various asphalt pavement materials. Saudi Arabia relies heavily on crude oil for power generation and desalination, resulting in significant COFA waste production. Currently, this waste is disposed of in sanitary landfills, posing risks of groundwater contamination and environmental pollution. This research evaluates the potential of recycling COFA as a filler material in asphalt pavement. The findings demonstrate that using COFA enhances several performance aspects of asphalt materials, provides a sustainable disposal method for fly ash, and reduces production costs in the road pavement industry. The bitumen content increases slightly with the increase of COFA this is due to the more fineness of COFA compared with fine aggregate. The lower specific weight of fly ash compared with aggregate needs more binding material. The tensile strength of asphalt containing COFA decreases with increasing COFA content but it is still within the performance level required. The stability of asphalt containing COFA shows better performance at high temperatures which could be an additional advantage, especially in hot weather such as in KSA.