Atomic Force Microscope (AFM) is a relatively new technique for investigation of construction materials.In this study AFM was used to investigate the interaction of asphalt binder with fly ash.Fly ash is a coal combustion byproduct of electric power utilities having pozzolanic properties and commonly used in Portland cement concrete.In this study,an investigation was made by using different types of fly ash with two types of asphalt binders such as PG 58-28 and PG 64-28.Asphalt microstructure is divided into four subgroups such as Saturates,Aromatics,Resins and Asphaltenes (SARA).These four phases can be distinguished by the atomic force microscope.The interaction of these phases affected by introducing fly-ash was investigated and correlation with rheological properties was observed.