Novel electro-conductive and mechanically-tough double network polymer hydrogels (E-DN gels) were synthesized by polymerization of 3, 4-ethylenedioxythiophene in the presence of a double network hydrogel (DN gel) matrix. The E-DN gels showed not only excellent mechanical performance, having a fracture stress of 1.42.1 MPa, but also electrical conductivity as high as 10-3 S cm-1, both under dry and water-swollen states. The fracture stress and fracture energy of the E-DN gel was increased by 1.7 and 3.4 times, respectively, as compared with the DN gel. From scanning electron microscope and AFM observations, it was found that electro-conductive poly(3,4-ethylenedioxythiophene) (PEDOT) was incorporated into DN gel matrix, apparently due to the formation of a poly-ion complex with sulfonic acid group of the DN gel network. Thus, PEDOT incorporated into the DN gel matrix greatly improves not only electronic conductivity, but also mechanical properties, reinforcing the double network gel matrix. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012