The present invention can sufficiently suppress curling phenomenon of a recorded product and facilitate handling of a printed product produced by using plain paper, in particular. The present invention provides a printing medium coating solution including water and a water-retentive, water-soluble organic compound, wherein the water-soluble organic compound includes only a water-soluble organic compound showing a difference of 36% or less between the water retention ability at a temperature of 23.degree. C. and a humidity of 45% and the water retention ability at a temperature of 30.degree. C. and a humidity of 80%; and the content of the water-soluble organic compound is 15 mass % or more with respect to the total amount of the printing medium coating solution. The present invention provides an ink-jet ink including a coloring material, water, and a water-retentive, water-soluble organic compound, wherein the water-soluble organic compound includes only a water-soluble organic compound showing a difference of 36% or less between the water retention ability at a temperature of 23.degree. C. and a humidity of 45% and the water retention ability at a temperature of 30.degree. C. and a humidity of 80%; and the content of the water-soluble organic compound is 15 mass % or more with respect to the total amount of the ink-jet ink.