The spherical LiFePO4/C and LiFe0.9Mg0.1PO4/C powders were successfully prepared from spherical FePO4 via a simple uniform-phase precipitation method at normal pressure, using FeCl3 and H3PO4 as the reactants. The FePO4, LiFePO4/C, and LiFe0.9Mg0.1PO4/C powders were characterized by scanning electron microscopies (SEM), powder X-ray diffraction (XRD), X-ray photoelectron spectrometer (XPS), and tap-density testing. The uniform spherical particles produced are amorphous, but they were crystallized to FePO4 after calcining above 400 °C. Due to the homogeneity of the basic FePO4, the final products, LiFePO4/C and LiFe0.9Mg0.1PO4/C, are also significantly uniform and the particle size is of about 1 μm in diameter. The tap-density of the spherical LiFePO4/C and LiFe0.9Mg0.1PO4/C are 1.75 and 1.77 g cm−3, respectively, which are remarkably higher than the non-spherical LiFePO4 powders (the tap-density is 1.0–1.3 g cm−3). The excellent specific capacities of 148 and 157 mAh g−1 with a rate of 0.1 C are achieved for the LiFePO4/C and LiFe0.9Mg0.1PO4/C, respectively. Comparison of the cyclic voltammograms of LiFePO4/C and LiFe0.9Mg0.1PO4/C shows enhanced redox current and reversibility for the sample substituting Mg on the Fe site. LiFe0.9Mg0.1PO4/C exhibits better high-rate and cycle performances than the un-substituted LiFePO4/C.