A new epoxide-terminated hyperbranched polyether sulphone (EHBPES) was synthesized using simple one-pot A(2)+B-3 approach. This highly effective toughener can toughen diglycidyl ether of bisphenol A/triethylenetetramine (DGEBA/TETA) curing system without forming phase-separated morphology. Effects of molecular weight (MW) and loading amounts on the mechanical and thermal properties of cure hybrids were investigated. The MW plays an important role in determining the crosslink density and defects of cured networks. Addition of medium-MW EHBPES-2 not only significantly improves toughness and elongation at break but also increases tensile strength and T-g. At 5 wt% loading of EHBPES-2, the cured hybrid shows an elongation at break of 15.3%, impact strength of 50.9 kJ/m(2), and tensile strength of 80.0 MPa. The simultaneous improvements are explained by the higher crosslink density, increased nano-scale cavities, and the inhomogeneous structure of the cured network. (C) 2015 Elsevier Ltd. All rights reserved.