This study aims to improve the rheological properties of AL-Dura Refinery asphalt using cellulose acetate as a natural polymeric additive. The asphalt was mixed with cellulose acetate in various proportions (1, 2, 3, 4,5, and 6%), and the mixture was stirred at 150 °C for 60 min. The rheological properties of asphalt, on the other hand, were modified by using cellulose acetate in the presence of 1% sulfur, and the mixture was stirred for 60 min at 180 °C. The physical characteristics of the modified materials, such as ductility, softening point, and penetration index, were determined. For some of the models, the Marshall Quotient, aging, and chemical immersion tests were also performed. The best models were tested using IR and HNMR spectroscopy, as well as thermal measurements (Tga, Dta, DSC, Tg). The obtained models have rheological properties that make them suitable for a variety of applications, including paving, moisture barrier construction, and flattening. In addition, the modified asphalt is less affected by ageing conditions compared with the original asphalt, especially in terms of weight loss percentage. This is considered as a critical aspect of using cellulose acetate in the modification process.