The synthesis of reduced graphene oxide (RGO) with various reduction extents was carried out in organic solvent using 1,4-diiodobutane as the reducing agent at moderate temperatures. Results showed that the C/O ratio of RGO nanosheet surface could be tailored by adjusting the ratio of graphene oxide (GO) and reducing agent. The controllable reduction strategy was applied to the fabrication of high dielectric constant graphene/polyimide composites via the in situ reduction of GO. The reduction extents of RGO in polymer matrix can be readily manipulated just through altering the addition of the reducing agent. The dielectric constants of gaphene/polyimide composites were significantly enhanced with the increasing of the reduction extent of RGO. Moreover, the mechanical properties of the composites were also affected by the reduction extent of RGO due to the decreases of the oxygen functional groups of RGO surface. Hence, the in situ controllable reduction of GO should be quite an ideal method for the fabrication of high dielectric constant composites with the tunable combination properties. (C) 2017 Elsevier B.V. All rights reserved.