To provide an aqueous black ink composition which is used in inkjet recording and writing implements, has a neutral hue and is black high in printing density, further excels in ozone resistance, light resistance, and water resistance, and has good storage stability as a recording fluid.

The aqueous black ink composition is a black ink composition comprising a water-soluble monoazo compound represented by formula (1) or its salt. The compound of formula (1) is also used as a color matching dye.