Fly ash (FA) is a porous ceramic, which has proved to have some favorable functions. In this article, we have prepared a series of fly ash filled composites, where the polyurethane-(PU) modified epoxy (EP) was acted as the matrix. With the purpose of characterizing the effect of the content of PU in the matrices and the surface-treatment (ST) of fly ash particulates on the dynamic mechanical properties of composites, Fourier transform infrared spectral analysis (FTIR), microstructure observation, impact property test as well as dynamic mechanical analysis (DMA) were systematically investigated. With FTIR test, it can be found that the chemical reactions occur, and new chemical structures are formed between EP and PU, and the functionalized groups existing on the surface of fly ash particulates can also be detected. In fractographs observation of composites, it can be seen that the silane coupling agent improves the interfacial bonding conditions between fly ash particulates and the matrix. Impact property test result reveals that PU improves the toughness of EP. Dynamic mechanical analysis of the composites is carried out from -40 to 150 degrees C using a tension-compression mode. Results show that the composites, whose matrices are with 10 and 20 wt % PU, may possess better dynamic mechanical properties as compared with the other composites. (c) 2007 Wiley Periodicals, Inc.