We report a simple and rapid method to synthesize graphene-modified Li3V2(PO4)3 as cathode material for lithium-ion batteries via microwave irradiation. By treating graphene oxide and the precursor of Li3V2(PO4)3 in a commercial microwave oven, both reduced graphene oxide and Li3V2(PO4)3 could be simultaneously synthesized within 5min. The structure, morphology and electrochemical performances of as-synthesized graphene-modified Li3V2(PO4)3 are investigated systematically by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, charge/discharge tests, electrochemical impedance spectra (EIS) and cyclic voltammetry (CV). The XRD result indicates that single-phase graphene-modified Li3V2(PO4)3 with monoclinic structure can be obtained. Both SEM and TEM images show that Li3V2(PO4)3 nanocrystals are embedded in the reduced graphene oxide sheets which could provide an easy path for the electrons and Li-ions during the cycling process. Compared with the pristine Li3V2(PO4)3 electrode, graphene-modified Li3V2(PO4)3 exhibits a better high-rate ability and cyclic stability. These superior electrochemical performances are attributed to the good conductivity of reduced graphene oxide which enhances the electrons and Li-ions transport on the surface of Li3V2(PO4)3. Thus, this simple and rapid method could be promising to synthesize graphene-modified electrode materials.