In this work, the influence of the new epoxy-containing liquid rubber-based modifiers on the thermal and mechanical properties of the cured epoxy resins was investigated. The epoxy-functional polybutadienes obtained via the conventional epoxidation reaction or catalytic hydrosilylation have been successfully applied for modification of commercially available epoxy resin to modulate its mechanical properties. Different locations of oxirane rings in the polybutadiene chains revealed a significant impact of the rubber-based modifier structure on the thermal and mechanical properties of cured resins.