An ink composition for ultraviolet curable ink jets including monomer A represented by a general formula (I): CH2=CR1-COOR2O—CH═CH—R3  (I) (in the formula, ‘R1’ represents a hydrogen atom or methyl group, ‘R2’ represents a divalent organic residue having a carbon number of 2 to 20, and ‘R3’ represents a hydrogen atom or a monovalent organic residue having a carbon number of 1 to 11), and a photopolymerization initiator containing an acylphosphine oxide-based photopolymerization initiator and a thioxanthone-based photopolymerization initiator, in which the total content of the acylphosphine oxide-based photopolymerization initiator and the thioxanthone-based photopolymerization initiator is 8% by mass to 16% by mass with respect to the total mass of the ink composition.