An object to be achieved by the present invention is to provide a binder for an ink-jet printing ink, the binder being capable of forming a printed image having excellent durability such as rubfastness and alkali resistance without impairing good ejection stability, storage stability, etc. of an ink, and an ink-jet printing ink containing the binder. The present invention relates to a binder for an ink-jet printing ink, the binder containing an aqueous medium (D); and a polyurethane (C) obtained by reacting a polyol (A) containing a vinyl polymer (a1) having two hydroxyl groups at one end and at least one polyol (a2) selected from the group consisting of polyether polyols, polyester polyols, polyester ether polyols, and polycarbonate polyols with a polyisocyanate (B), the polyurethane (C) having a structure derived from the vinyl polymer (a1) in a side chain thereof and being dispersed in the aqueous medium (D), and printed matter.