Like many other Mediterranean countries, Jordan is seeing an increase in olive tree cultivation as a result of the growing demand for olive oil worldwide. The process of extracting olive oil generates significant amounts of biomass waste from both industrial and agricultural sources. This waste is often used as a fuel source during cold seasons, leading to the production of large quantities of olive oil waste ash, a toxic substance typically disposed of in landfills. Improper disposal can pose environmental risks, including groundwater pollution, a critical impact on drinking water sources. This paper explores the potential of utilizing ash, a by-product of biomass waste from olive oil production, in order to enhance the properties of asphalt mixtures. Specifically, this study examines the use of two types of fly ash, class C and class F, as a filler in two types of bitumen and asphalt materials, AC40/50 and AC60/70. The rheological performance of asphalt modified with varying fly ash filler content, ranging from 0% to 10% in 2% increments, was tested. The results demonstrate that incorporating fly ash improves the rutting resistance of asphalt, which could reduce the costs associated with pavement repair and rehabilitation, while also mitigating the environmental impact of disposing of large amounts of toxic fly ash waste.