To provide a UV light excitation type ink composition which is substantially invisible in the visible light region, does not deteriorate the appearance of an article, when printed on the article, makes it possible to highly sensitively detect the printed mark without being affected by the color of a substrate, is safe for human bodies, is never limited by use environments, and can give images having high light resistance.

This ink composition which comprises an europium-containing pigment which is substantially invisible in the visible light region and is excited with UV light to emit light having a central emitted light wavelength of 615±20 nm, and a polyvinylic resin, and further contains ≥94 wt.% of ethanol in a solvent, characterized by containing both (a) an antioxidant and (b) a hindered amine photostabilizer and/or a sulfur compound.