An ink composition including a cationically polymerizable compound (a), a
compound (b) that generates acid by irradiation with a radiation ray, and
a basic compound (c) that becomes less basic by irradiation with a
radiation ray. Also, an inkjet recording method and a printed material
using the ink composition, as well as a planographic printing plate
obtained by using the ink composition and a method of producing the
planographic printing plate are disclosed.