In the biphenol-type epoxy resin cured with catechol novolac (CN), a very weak glass transition and, thus, a very high rubbery modulus were observed. On the other hand, the glass transition was clearly observed in the system cured with phenol novolac (PN). This means that the micro-Brownian motion of network chains is highly suppressed in the system cured with CN. The reason for this suppression of the chain motion in the CN-cured system has been pursued from the viewpoint of the conformation of network chains. The disappearance of the glass transition in the biphenol-type resin depends on the formation of the active hydrogens in the curing agents. Thus, it was suggested that the suppression of the micro-Brownian motion is due to the orientation of the biphenyl groups in the network. Moreover, it has been shown that the mechanical and bonding strength at high temperature is considerably improved by the suppression of the network chain motion in the CN-cured biphenol resin system.