To understand the delithiation behavior of particles of different sizes, we developed a centrifugation method to separate particles in a chemically-delithiated Li0.49FePO4 with respect to their size. Small particles were obtained at high centrifuge speed whereas large particles were obtained at low centrifuge speed. The proportions of FePO4 and LiFePO4 in the separated particles were investigated to understand their delithiation behavior. Small particles were almost fully-transformed to FePO4 whereas large particles were still mostly LiFePO4. The inhomogeneous delithiation of particles could be also observed in the electrode. The electrode showed a voltage overshoot in the middle of the two-phase region during charging. Considering that the voltage overshoot is related to nucleation, this observation indicates that some particles in the middle of two-phase region are still in the LiFePO4 phase that must be nucleated. The inhomogeneous delithiation behavior of LiFePO4 particles of different sizes may be an intrinsic property irrespective of the delithiation method. To improve the utilization of active materials, the inhomogeneous delithiation of particles should be minimized by engineering the configuration of the electrode.