Abstract: There is provided a pigment dispersant that is a block polymer P in which a hydrophobic polymer block A and a hydrophilic polymer block B containing an anionic group are linked to each other. The block polymer P has a number average molecular weight ranging from 1000 to 4000; and where the block polymer P is subjected to 100% neutralization of the anionic group with a basic compound and dispersed in water and where the fine particles of the dispersed block polymer P are subjected to measurement of a scattering profile by small- or ultra-small-angle X-ray scattering that involves use of synchrotron radiation, at least one minimum value in the scattering profile is present within the range of a scattering vector q from 0.1 to 1 nm?1. There is also provided an aqueous pigment dispersion containing the pigment dispersant, a pigment, a basic compound, and an aqueous medium.