At present, there is no accepted standard by highway authorities on the compaction procedures of 100mm-diameter gyratory compactor specimens. In previous studies on gyratory compaction, the method of either coring from 150mm specimens, or preparing taller specimens than the usual 63.5mm-long Marshall specimens, has been undertaken. However, the utilisation of 150mm-moulds produces a significant amount of mechanical disturbance during the coring process of 100mm-diameter specimens. The note-worthy aspect of this study is that a new standard for preparing gyratory compactor specimens with a diameter of 100mm and a length of approximately 63.5mm has been proposed for the first time. In this study, the design gyration number of the asphalt mixture was obtained by carrying out extensive laboratory testing on the specimens prepared, and by changing various testing parameters including the gyration number, angle of gyration, specimen height, and ram pressure. First, tests using 600kPa ram pressure and a 1.25 degrees gyration angle with varying gyration numbers were carried out. Then, the gyration angle was changed from 1.25 degrees to 1.85 degrees by 0.05 degrees increments. Following that, a completely different pattern of loading level using 240kPa with a 2 degrees gyration angle was investigated. And finally, changing the gyration angle from 1.60 degrees to 2.40 degrees by 0.20 degrees increments was carried out to provide a wider scope of investigation. As a result, the design gyration number for 100mm-diameter asphalt mixtures was determined as 40 under medium traffic conditions.