The flexible pavement use for many roads in Indonesia. The mostly of flexible pavements used asphalt binder material derived from petroleum refineries, while in Indonesia has natural resources of natural asphalt or commonly called Aspal Buton. One of the asphalt buton process is Retona Blend 55 asphalt which can be found from result between penetration asphalt 60 and 80 with asbuton processed semi extraction. In asphalt mixture usually using stone ash as a filler. But in this research using fly ash. Parameter Marshall Test in this study using Spesifikasi Umum 2010 (Revisi 3) is used to know the quality of AC-WC. This study was conducted to determine the effect of utility fly ash as a mixture of asphalt concrete in wearing course. The parameters assessed are stabillity, flow, VIM, VMA and MQ. The result of KAO test obtained is 6% and the percentage of fly ash as a filler are 5%, 5,5%, 6%, and 6,5%. The result of Marshall Test showed that value of VIM and VMA have tendency to decrease with increasing of percentage of fly ash, but the value of VFA have tendency to increase. From the comparison of stabillity and flow values, Marshall Quotient without fly ash amounted to 642.58 kg / mm and using fly ash 5% amounted to 558.80 kg / mm.