This study aims to investigate the effect of polytriazolesulfone(PTS) addition on fracture toughness of diglycidyl ether of bisphenol A(DGEBA) and 4,4’-diaminodiphenylsulfone( DDS). Various amounts of PTS were added to DGEBA/4,4’-DDS in diazide and dialkyne monomer forms and polymerized during the epoxy curing process. Fracture toughness(K1C), tensile properties and thermal stability of the PTS added epoxy resin were evaluated and compared with those of PES, the conventional high Tg toughening agent, added epoxy resin. Fracture toughness of the PTS added epoxy resin was dramatically improved up to 133%, as the amount of PTS added increased, whereas that of the PES added epoxy resin was improved by only 67%. The tensile strength of PTS added DGEBA/4,4’-DDS was similar to the epoxy resin without PTS and tensile modulus was improved by 20%. And thermal stability of the PTS added epoxy resin was improved up to 14%. Therefore, PTS addition to DGEBA/4,4’-DDS, as a toughening agent, is very effective way to improve its fracture toughness without any lowering in other properties.