Abstract: To solve the conflict about the effects of particle size on magnetost rictive properties of polymer-bonded Terfenol-D composites studied by different scholars, Terfenol-D/unsaturated polyester resin composites were prepared with 20 % volume fraction Terfenol-D powders in six particle-size ranges (30～53μm, 53～150μm, 150～300μm, 300～450μm, 450～500μm and 30～500μm). The static and dynamic magnetostrictive properties, magnetomechanical coupling coefficient, Young modulus and compressive strength were tested. The results indicate that the composite with particles of 53～150μm distribution presents the largest static and dynamic magnetostrictive properties among all the five monodispersed distribution samples. The sample with particle size in 30～500μm shows even larger response than that with 53～150μm particle size distribution. It indicates that the particle size plays a double-edged sword on magnetostrictive properties of magnetostrictive composites. The existence of the optimal particle size to prepare polymer-bonded Terfenol-D composites results from the competition between the positive effects and negative effects of increasing the particle size.