Amorphous and crystalline FePO4 were synthesized by annealing the precursor aqueous solution with P2O5 and iron powder in air. Although planetary ball milling is effective for reducing the synthetic time, it was confirmed that 15 days were sufficient reaction time, even at room temperature, to bring the same result without mixing. Annealing at over 500°C in air resulted in trigonal FePO4 with a P321 space group. Both amorphous and crystalline FePO4 have a corner-shared matrix, and they showed similarly good capacity, not only for Li but also for Na anodes.