The effect of low-molecular polysulfones (oligosulfones) on the static and dynamic relaxation properties of epoxy polymers based on industrial resin ED-20 is studied. It is established that the modification of oligosulfones with terminal carboxyl, phenolic groups and a molecular weight from 1200 to 44500 leads to the formation of epoxy systems with higher performance in terms of development of static processes of creep and stress relaxation. It is demonstrated that the dynamic shear modulus increases with the introduction of the modifier. The magnitude of this effect is proportional to the molecular weight of oligosulfones. The intensities of the high-temperature α-transition at 390 K and the low-temperature β-transition at 208 K decrease with the introduction of the modifier. The improvement of the relaxation properties is associated with an increase in the density of the chemical grid of the epoxy matrix with the introduction of modifiers, its saturation with more rigid and heat-resistant component and the formation of additional intermolecular bonds between the components of the system