The precursors of LiFePO4 were prepared by a sol–gel method using lithium acetate dihydrate, ferrous sulfate, phosphoric acid, citric acid and polyethylene glycol as raw materials, and then the carbon-modified nanocrystalline LiFePO4 (LiFePO4/C) cathode material was synthesized by a one-step microwave method with the domestic microwave oven. The effect of microwave time and carbon content on the performance of the resulting LiFePO4/C material was investigated. Structural characterization by X-ray diffraction and scanning electron microscopy proved that the olivine phase LiFePO4 was synthesized and the grain size of the samples was several hundred nanometers. Under the optimal conditions of microwave time and carbon content, the charge–discharge performance indicated that the nanosized LiFePO4/C had a high electrochemical capacity at 0.2C (152mAhg−1) and improved capacity retention; the exchange current density was 1.6977mAcm−2. Furthermore, the rate capability was improved effectively after LiFePO4 was modified with carbon, with 59mAhg−1 being obtained at 20C.