Mn(III) doped Li3V2-xMnx(PO4)3/C (x=0.2) is prepared by sol-gel method. Mn(III) is well substituted the position of V in Li3V2(PO4)3 (LVP) without any Mn-contained impurity phase. The crystal structure and morphology in Mn-substituted Li3V2(PO4)3 are studied by X-ray diffraction patterns (XRD), XPS and scanning and high-resolution transmission electronic microscopy (SEM and HRTEM). Mn(III) substitution increases the electrochemical performance of Li3V2(PO4)3 at high cut-off voltage of 4.8V. Li3V1.8Mn(III)0.2(PO4)3 delivers 185 mAh g−1 at 0.1C, close to the theoretical capacity of Li3V2(PO4)3, and delivers initial capacities of 130 and 126 mAh g−1 at 5C and 10 C-rate, remaining 95% and 97% of the initial capacities after 100 cycles when charged to 4.8V. Mn(III) plays an important role in maintaining the three-dimensional (3D) solid framework structure to provide an improved cycle life at higher cut-off voltage of 4.8V and improving the high-rate performance of Li3V2(PO4)3.