: In the past decades modifiers of bitumen have been used for increasing asphalt concrete quality in this way fibers can be used widely because of favorable physical and chemical properties as well as their proper-mixing with bitumen. The main aim of this study is therefore to enhance the quality of asphalt concrete by using Polypropylene fiber in monofilament form, for this purpose different lengths, percentages and fines of fibers were used . consequently, the optimized values of fiber length, fiber fines and fiber percentage were obtained. optimized percentage of fiber lengths of 3.75 , 7/5,15,30 mm were selected and finally the optimized efficient length was determined. Specific weight test , marshal stability and flow value have been obtained for all tested samples. Efficient percentage of fibers at different fines of 340 , 680 , 1700 (denier) were 1%, 2%, 4% , respectively .In fact , the more the fiber fines leads to the higher efficient percentage moreover by comparing the asphalt concrete samples which reinforced by fibers , the one with 4% fiber and 1700(denier) fines proposed the most marshal stability however maybe the asphalt concrete sample with 1 % fiber and 340 (denier) is more economical overall, discreet monofilament fibers don’t have a great impact on the marshal stability test results but by increasing the percentage of fibers, flow values increased and specific weight result decreased.
