To provide an ink for use in ink-jet printing which has improved resistance to water and staining, and, particularly in a pigment-based ink, can maintain stable dispersion and high pen relinability even when such improvement is performed, by incorporating, in an aqueous carrier medium, an insoluble colorant, a polymer dispersant and a hydrosol polymer.

(a) An aqueous carrier medium is a mixture of water and one or more of water-soluble organic solvents. A mixture of water and a polyhydric alcohol (for example, diethylene glycol) is preferred. This component has a water content of 60 to 95wt.% and accounts for 70 to 99.8% of the total ink composition. (b) This component is a dye or a pigment which is insoluble in component (a). This component is a colorant which is insoluble over the whole process of printing. A pigment is preferred. (c) Suitable polymer dispersants include a random polymer, such as a block polymer or a branched polymer, and a structured polymer. (d) A hydrosol polymer is first synthesized in an organic solvent and then is dispersed in component (a).