The effects of volume fraction, particle size, and surface state of AI(OH)(3) fillers on the dynamic mechanical properties of EPDM/Al(OH)(3) composites were investigated by dynamic mechanical analysis (DMA). The interfacial structure parameters of EPDM/Al(OH)(3) composites were also investigated. The results show that dynamic mechanical property and the glass-transition process of composites are distinctly influenced by the volume fraction, particle size, and surface state of Al(OH)(3) fillers. With the increase of volume fraction and decrease of particle size of Al(OH)(3) fillers, the temperature corresponding to the maximum damping factor of composites shifts to a higher temperature with lower peak value and broader half-peak width. The treatment of fillers with coupling agent can greatly enhance two-phase interaction and thus improve the dynamic mechanical properties of composites. Consequently, a lower damping factor, broader half-peak width, and larger apparent activation energy of glass transition can be achieved. In addition, a novel method of calculating the apparent activation energy of composites is put forward based on the DMA method, which has been verified by calculating the apparent activation energy of glass transition of Al(OH)(3)-filled EPDM composites. (c) 2005 Wiley Periodicals, Inc.