To provide a reactive liquid with excellent resolubility and an ink set which includes the reactive liquid for forming an image in high color development properties and an ink.

The ink set is composed of the ink (1) containing an anionic coloring material and the reactive liquid (2) containing a cationic substance (4) which promotes the flocculation of the anionic coloring material and a water-soluble polymer compound (5). In addition, the water-soluble polymer compound has at least, a repeated structural unit containing a monomethyl maleate as a monomer component and a repeated structural unit containing a vinyl alcohol as a monomer component.