This invention provides a water soluble azo compound for yellow represented as a free acid by formula (1): [Chemical formula 1] (1) wherein A represents a hydroxyl group, a morpholino group, an amino group, an optionally substituted aliphatic amine residue, an optionally substituted aromatic amine residue, an optionally substituted phenoxy group, or an optionally substituted alkoxy group; R1 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; R2 represents a hydrogen atom, a nitro group, or a hydroxyl group; and n is an integer of 1 to 3, and an ink composition comprising the water soluble azo compound. The ink composition is highly stable, is suitable for ink jet printing, and can yield printed matter having a very high level of various fastness properties such as ozone resistance.