Graphene is an excellent material for flexible electronics due to its high carrier transport properties. We report a flexible graphene field effect transistor on polyimide substrate using graphene oxide as top-gate dielectric. Good current saturation and peak hole and electron mobilities of 496 cm2/(V.s) and 164 cm2/(V.s) are observed, respectively, for the proposed intrinsic RF device. A maximum transconductance of 0.42 mS and the intrinsic cutoff frequency of 117 GHz are achieved when the gate length is reduced up to 0.25 μm.