To provide a pigment ink capable of making the high water resistance of printed images and the ink's long-term storage stability improvement compatible with each other, and to provide an ink-jet printing method, an ink cartridge, a printing unit and an ink-jet printer each using the ink.

The pigment ink contains, at least, a pigment, a modified siloxane compound, and an alkanediol. In this ink, the pigment has ionic groups on the pigment particles, wherein the ionic group density on the pigment particles is 0.7 mol/m2 or higher but lower than 1.5 mol/m2, and the modified siloxane compound has a specific structure, weight-average molecular weight and HLB number.