It is an object of the present invention to provide a yellow ink composition which is superior in terms of color reproducibility not only in the high-brightness (high-L*) region, but also in the low-brightness yellow region, i.e., in the region of "low L*, a* close to zero, and high b*", and an ink set equipped with a yellow ink which has a brightness that is high enough that graininess can be sufficiently suppressed, and which is also superior in terms of color reproducibility in the low-brightness yellow region, i.e., in the region of "low L*, a* close to zero, and high b*". The present invention provides a yellow ink composition in which the Y value is 86 or greater when the Z value in the XYZ display system stipulated by the CIE is 23. Furthermore, the present invention also provides a yellow ink composition which contains a metal complex pigment. In particular, the yellow ink composition of the present invention can express a low-brightness yellow color with good reproducibility. Moreover, the present invention provides an ink set containing a yellow ink in which the Y value is 86 or greater when the Z value in the XYZ display system stipulated by the CIE is 23, as calculated from the ultraviolet-visible transmission spectrum of an aqueous solution diluted 10,000 times by weight or lower.