The Li2MnSiO4/C nanocomposite has been successfully synthesized at a relatively low temperature of 650 °C by a facile solid-state reaction using citric acid as the carbon source. The highly crystalline Li2MnSiO4 nanoparticles in the size of 20–50 nm are coated by a uniform carbon layer in a thickness of 2–5 nm. At a rate of 0.05 C, the Li2MnSiO4/C nanocomposite exhibits a discharge specific capacity as high as 268 mAh g−1 for the first cycle and a reversible capacity of about 136 mAh g−1 after 140 cycles at room temperature. Meanwhile, an improved rate performance is achieved by the Li2MnSiO4/C nanocomposite. These superior electrochemical properties could be attributed to the nanoscale particle size and the enhanced electronic conductivity.