<p>Polyhedral oligomeric silsesquioxane (POSS) combines the advantages of inorganic nanoparticles and organic flexible segments, enabling the enhancement of the comprehensive properties of epoxy resins. POSS grafted with organic groups can serve as a good toughening curing agent for epoxy resins. In this paper, D/A (polyetheramine D230/aniline) series and D/B (polyetheramine D230/n-butylamine) series co-grafted POSS toughening curing agents were prepared. A series of epoxy resins cured with different curing agents were further prepared. The influence of the structure of grafted small molecule amine and the ratio of polyetheramine/small molecule amine on the properties of cured epoxy resins was discussed. The research results indicated that cured epoxy resins exhibited excellent properties. The toughening effect of curing agent D/A4/OP is the best. Compared to epoxy resins cured with polyetheramine D230, the impact strength maximum increased from 46.3 to 78.2&#xa0;kJ&#xa0;m⁻², an increase of 68.9%; the fracture toughness maximum increased from 15 to 24.8 kPa&#xa0;m¹/², an increase of 65.3%. The toughening curing agents combine the advantages of rigid POSS and flexible polyetheramine. By regulating the side chain structure, distribution, and grafting amount of grafted POSS, the toughness of epoxy resins has been significantly improved. This is due to the synergistic toughening effect of the three-dimensionally distributed flexible polyether segments and the rigid POSS particle structure within the co-grafted POSS. The epoxy resins cured with the toughening curing agents have great potential and applicability, with broad application prospects.</p> Graphical Abstract <p></p>