<p>This study investigates the influence of diamond content on the strain rate-dependent mechanical properties of epoxy matrix composites. Quasi-static and dynamic compression tests revealed that epoxy materials with varying diamond contents all exhibited significant strain rate sensitivity: the elastic modulus increased substantially with rising strain rates, demonstrating pronounced viscoelastic characteristics. At identical strain rates, the mechanical performance initially enhanced but subsequently declined with increasing diamond content. Notably, composites containing 5 wt.% diamond displayed inferior properties compared to pure epoxy. The nonlinear viscoelastic Zhu-Wang-Tang constitutive model was employed to derive and fit material-specific parameters, enabling accurate prediction of the elastic behavior in diamond/epoxy composites. Fractographic characterization indicated that diamond particles enhance energy absorption by hindering crack propagation and generating voids through interfacial debonding. However, excessive particle content induces agglomeration, which would compromise the mechanical integrity of the composites.</p> Graphical Abstract <p></p>