A high performance thermosetting epoxy resin crosslinkable at room temperature was obtained via directly moulding diglycidyl ether of bisphenol A (DGEBA) and flexible α,β-bisamino(n-alkylene)phenyl terminated poly(ethylene glycol). The influences of the n-alkylene inserted in aminophenyl of flexible amino-terminated polythers (ATPE) on the mechanical properties, fractographs and curing kinetics of the ATPE-DGEBA cured products were studied. The results show that the insertion of n-alkylene group into the aminophenyl group of the ATPE, on one hand, can significantly increase the strain relaxation rate and decrease glass transition temperature of the ATPE-DGEBA cured products, resulting in slight decrease of the Young’s modulus and tensile strength, and significant increase of the toughness and elongation of the ATPE-DGEBA cured products. On the other hand, it can remarkably enhance the reactivity of amine with epoxy, much accelerating the curing rate of the ATPE-DGEBA systems. The activation energy of DGEBA cured by BAPTPE, BAMPTPE and BAEPTPE was 53.1, 28.5 and 25.4 kJ.mol-1, respectively. The as-obtained ATPE-DGEBA cured products are homogeneous, transparent, and show excellent mechanical properties including tensile strength and toughness. Thus they are promising to have important applications in structure adhesives, casting bulk materials, functional coatings, cryogenic engineering, damping and sound absorbing materials.