<p>The study employs a dynamic mechanical analyzer&#xa0;to investigate the frequency-dependent viscoelastic properties of epoxy composites reinforced with spherical particles and milled glass fibers. This investigation examined 10% milled fiber and 15% spherical particle-filled epoxy composites that were the optimized volume fractions of glass fillers based on compression experiments. The composites were subjected to frequency-sweep tests from 10&#xa0;Hz to 0.1&#xa0;Hz at temperatures between 30&#xa0;°C and 110&#xa0;°C. The 10% milled fiber composites showed higher frequency-swept storage modulus (<i>E'</i>) values than 15% spherical composites at all temperatures, suggesting that the higher aspect ratio of miller fibers increases polymer chain entanglement with fibers, impeding their mobility, unlike spherical particles, which may allow rigid body rotation in the matrix. Time–temperature superposition principles were used to generate master curves for neat epoxy and glass-filled composites by integrating <i>E'</i> values across various experimental frequency and temperature ranges to predict <i>E'</i> values beyond the experimental operating frequencies. The 10% milled fiber composite exhibits ~ 25% and ~ 65% rise in <i>E'</i> values over 15% spherical particle composite and neat epoxy, respectively, particularly at higher reduced-frequencies (or at temperatures below the epoxy’s glass transition temperature (<i>T</i>_<i>g</i>)). The lower <i>E'</i> values of 15% spherical composites over neat epoxy at higher reduced-frequencies (or at temperatures below epoxy’s <i>T</i>_<i>g</i>) are corroborated by filler/matrix debonding witnessed in the scanning electron micrographs. The Prony series function, in conjunction with skewed Gaussian variation of relaxation modulus and relaxation time, accurately represented the experimental <i>E'</i> master curve data.</p>