This study presents the preparation of Li3V2(PO4)3/C composite material by using a hydrothermal method and post-thermal treatment. By adding a 5 wt.% polystyrene (PS) sphere and a 2 wt.% carbon sphere (CS) to the Li3V2(PO4)3/C composite material, the rate capability and cycle performance stability greatly improved. The characteristic properties of the Li3V2(PO4)3/C composite material were examined using X-ray diffraction (XRD), micro-Raman spectroscopy, scanning electron microscopy (SEM), an AC impedance method, and a galvanostatic charge–discharge method. For comparison, Li3V2(PO4)3/C composite material without CS fillers was also prepared. Thus, the Li3V2(PO4)3/C composite material with a 5% polystyrene sphere and a 2% CS displayed discharge capacities of 195, 171, 165, 158, 149, 140, and 90 mAh g−1 at rates of 0.1, 0.2, 0.5, 1, 3, 5, and 10 C, respectively. Even at a 1 C discharge rate for 30 cycles, the composite presented a capacity of 151–142 mAh g−1 and excellent cycling performance with a fading rate of 0.195% per cycle. The outstanding performance was attributed to the particular morphology and uniform carbon-layer coating of the Li3V2(PO4)3/C composite material, which proved to be a suitable candidate for application in Li-ion batteries.