To provide an actinic-radiation-curing composition and an actinic-radiation-curing ink each of which is excellent in storage stability and can give a highly sharp recorded image excellent in character quality and free from color bleed under various environments and to provide an image formation method and an inkjet recorder.

The actinic-radiation-curing composition contains (A) a photo acid generator, (B) an oxetane-ring-containing compound represented by formula (1), and (C) a sensitizer which is at least one member selected from among a polycyclic aromatic compound, a carbazole derivative, and a thioxantone each of which may be substituted with a hydroxyl group or an aralkyloxy or alkoxyl group which may be substituted and has an ultraviolet spectrum absorption at a wavelength longer than 300 nm. In formula (1), R1 to R6 are each a hydrogen atom or a substituent, provided that at least one of R3 to R6 is a substituent.