We investigated the mode 11 fracture toughness (K-IIc) with time and temperature dependence of the bisphenol A type of epoxy resin. We performed an asymmetric four-point bending test under various conditions of temperature and displacement rate. We found that K,,c strongly depended on the displacement rate and the temperature, even at room temperature. Moreover, it was governed by the time-temperature equivalence principle in re-gard to the fracture time. The time-temperature dependency of K-IIc was similar to that of the loss modulus (E''), and the transition of brittle to ductile fractures occurred nearly simultaneously when F peaked. (C) 2005 Wiley Periodicals, Inc.