Utilizing gyratory compaction technique for the preparation of asphalt specimens with 100 mm diameter moulds is an effective and realistic way of pavement laboratory testing. In fact, Marshall compaction is not a suitable way of modelling in situ conditions in the laboratory environment. Therefore, there has to be some means especially for the determination of the optimal addition of modifier amount which is multifilament 3 mm polypropylene (PP) fibers in this case for asphalt specimens prepared via gyratory compaction. Mechanical differences of reference and various amounts of PP modified asphalt mixtures were compared using Superpave gyratory compaction method by carrying out static creep tests utilizing Universal testing machine and standard physical properties, Marshall stability and flow analyses. Also, these test results were compared with the results previously obtained for similar sets of asphalt specimens compacted by 50 blows of Marshall hammer. By carrying out extensive analyses, it was not only seen that the utilization of PP fibers improves the physical and mechanical properties of the resultant mixture mainly by improving the permanent deformation resistance, but also the optimal amount of addition of the aforementioned PP fibers was found to be again 5.5 parts per thousand by the weight of aggregate which is the same with the previous Marshall compaction test results. Finally, it is proven that the optimal fiber addition is independent of compaction technique which is very important for repeatability and reproducibility of the test results. (C) 2013 Elsevier Ltd. All rights reserved.