<p>Composite materials with epoxy resin matrix modified with micron particles of MgO, B₄C (1, 3, and 5 wt%) were considered. Experimental study of viscoelastic properties of the composites prepared was carried out by indentation method under different loading modes. Indentation diagrams obtained under different loading modes (loading/unloading rate, indenter holding time at constant load) were applied as input information in order to determine the viscoelastic properties of the composites. The influence of additives concentration, their microstructure on the viscoelastic properties was theoretically investigated (Prony series). A computational algorithm for predicting the viscoelastic properties of composites consisting of a linear viscoelastic matrix and elastic dispersed additives was developed. The approach proposed to the determination of viscoelastic properties of composite materials was experimentally confirmed for the composites studied.</p>