Decreasing particle size ensures a good accessibility for LiFePO4 to reach theoretical capacity and achieve high cycling rates owing to the improved Li-ion diffusion coefficient. In this paper, the size of LiFePO4 particle is successfully controlled hydrothermally through adjusting the size and morphology of its precursor precipitate via high shear mixer (HSM) without involving any environmentally toxic surfactants. It is indicated that the LiFePO4/C particles synthesized by HSM at the stirring rate of 1.3×104 rpm exhibit a reduced particle size of ∼220nm and an enlarged surface area of 15.6m2·g−1, which perform a high Li-ions diffusion coefficient of 1.43×10−13 cm2·s−1. The LiFePO4/C nanoparticles exhibit large discharge capacity of 160.1mAh·g−1 at 0.1C and even high rate capacity of 90.8mAh·g−1 at 20C. This work suggests that adjusting the size and morphology of the precursor precipitates is an effective way to quicken the nucleation and crystal growth, so that to obtain fine particles with high specific surface area and high crystalline purity.