Bisphenol-A type and biphenyl type epoxide resins were cured with two types of aromatic diamines which have or do not have the carbon bridge between aromatic rings. Internal stress of these cured resins decreased with the introduction of a biphenyl structure into the networks. This reduction of the internal stress is attributed to the decrease of the elastic modulus in the glassy region caused by the low mobility of the biphenyl segment. On the other hand, the glass transition temperature increased with increasing the concentration of the biphenyl unit in the networks. These results revealed that the consistency of the decrease of the internal stress with the improvement of the heat resistance of the cured systems is possible by introducing the biphenyl structure to the epoxide resin networks.