A novel LiMn0.8Fe0.2PO4/C composite is synthesized via a sol–gel process. In this composite, acetylene black is embedded in LiMn0.8Fe0.2PO4. The structure and morphology of the resulting composite are characterized with XRD, SEM, TEM, and BET, and its performance as the cathode of lithium ion battery is investigated by charge–discharge test and EIS, with a comparison of the sample prepared without embedding acetylene black. It is found that the embedded composite exhibits better performance than the non-embedded sample. The former delivers a reversible capacity of 160 mAh g−1, while the latter only 142 mAh g−1 at 0.1 C (1C = 150 mAh g−1 in the work). The embedded acetylene black not only functions as a barrier for the growing of LiMn0.8Fe0.2PO4 particles in the preparation process, which is important for the formation of nano-particles, but also helps build a stable conductive network, thus improving the charge–discharge performance of LiMn0.8Fe0.2PO4.