Pigment ink composition

A pigmented ink composition comprising a pigment, a resin having an acidic group and an organic solvent having a boiling point of at least 150° C. which is present in an amount of from 50 to 90% by weight based on the whole weight of the ink composition. When this ink composition is subjected to an printed layer-sliding test in which the ink composition is applied on a cationically treated printing medium with a #4 bar coater (available from TOYO SEIKI KOGYO CO., LTD.) and dried and then the printed surface is slid with a cloth on which a weight of 50 g is placed, the printed record is not grazed. This ink composition contains the pigment with a small dispersion particle size and has good water resistance, can be printed on a plain paper sheet without cockling, and suffers from no grazing of printed records when the ink composition is printed on a cationically treated paper sheet.