Exploring solid state electrolytes with high ionic conductivity and good electrochemical stability is of prime importance for the development of safe batteries. In this study, we prepare a high-performance "polymer-in-salt" solid polymer electrolyte (SPE) by using polyacrylonitrile (PAN) as a host polymer, bistrifluoromethanesulfonimide lithium salt (LiTFSI) as an electrolyte salt, and different loading graphene oxide (GO) as a nano-filler. PAN-LiTFSI electrolyte filled with 0.9 wt% GO nanosheet exhibits an ionic conductivity of 1.1 x 10(-4) S cm(-1) at 30 degrees C, which is almost one order of magnitude higher than that of the filler-free one. In addition, the anodic potential and the lithium ion transference number also increase to 5 V and 0.4, respectively. The enhancement on ionic conductivity is attributed to a 3D fast ion transport network constructed by GO nanosheets and a further decoupling of ion transport from segmental dynamics. (C) 2016 The Electrochemical Society. All rights reserved.