The invention provides an inkjet black ink ensuring excellent image durability capable of satisfactorily maintaining the image quality such as non-loosening of black and gradation even when the image is stored for a long period of time, which is a inkjet black ink having a discoloration rate constant (k.sub.vis) of 5.0.times.10.sup.-2 [hour.sup.-1] or less, which is measured by using an ozone gas, the ink comprising an aqueous medium having dissolved or dispersed therein at least one dye selected from (1) an azo dye having a specific structure where a heterocyclic group is bonded to both of two N atoms, (2) a phthalocyanine dye having a specific structure, (3) an azo dye having a specific structure where a 5-membered heterocyclic group is bonded to one of two N atoms and a 6-membered 2-amino heterocyclic group is bonded to the other, and (4) a bisazo dye constituted by a specific aromatic or heterocyclic group and an azo group.