An inexpensive fly ash (FA), which is from a waste production, has been employed to fabricate fly ash/epoxy composites in our work. Three kinds of fly ash with the most probable diameters of 74"m, 119"m and 146"m were filled in the modified epoxy resin (EP). The purpose of this study is to characterize the dynamic mechanical properties of such composites, and the dynamic mechanical behaviors of the composites are investigated in the temperature range from -40 to 150oC using a tension-compression mode. The results indicate that the dynamic elastic moduli for the fly ash/epoxy composites are (1.4~2.0) GPa, and the peak values of loss factor (tanδ) for these composites can reach (0.79~0.90) in the test specification. In addition, a scanning electron microscope (SEM) has been used to observe the distribution of fly ash particles in the matrix, as well as the photographs of fracture surface of composites.