A method for modifying a fine particle dispersion liquid with which dispersibility and dispersion stability can be improved includes performing filtration to remove impurities in a dispersion liquid using a dispersion liquid modifying device provided with a removal unit that uses a filtration membrane. The quantity of impurities is reduced from a first region until said quantity reaches a second pH-dependent region. In the second pH-dependent region, the dispersibility of the fine particles in the dispersion liquid is in a range in which the dispersibility depends more on a change in dispersion liquid pH than on a change in the quantity of impurities in the dispersion liquid. With the quantity of impurities reduced to the second pH-dependent region, the dispersibility of the fine particles is controlled by adjusting the pH of the fine particle dispersion liquid.