A liquid crystalline epoxy resin was cured under non- and 10T-magnetic fields, and polydomain and monodomain networks were obtained, respectively. The fracture toughness of these systems was evaluated and it was clarified that the toughness of the magnetic field system showed a higher value. To investigate the toughening mechanism, polarized micro FTIR measurements were carried out. As a result, it was clarified that their mechanisms were quiet different. (c) 2006 Wiley Periodicals, Inc.