A new type of epoxy resin containing 4,4'-diphenylether moiety in the backbone (2) was synthesized, and was confirmed by gel permeation chromatography, infrared spectroscopy, and H-1 nuclear magnetic resonance spectroscopy. In addition, in order to evaluate the influence of 4,4'-diphenylether moiety in the structure, epoxy resins having 4,4'-biphenylene moiety (4) and having 1,4-phenylene moiety (6) in place of 4,4'-diphenylether moiety were synthesized. The cured polymer obtained through the curing reaction between the new diphenylether-containing epoxy resin and phenol novolac was used for making a comparison of its thermal and physical properties with those obtained from 4, 6, and bisphenol-A (4,4'-isopropylidenediphenol) type epoxy resin. The cured polymer obtained from 2 showed markedly higher anaerobic char yield at 700 degrees C of 44.0 wt %, higher fracture toughness, and higher mechanical strength and modulus.