The ink composition of the present invention contains a coloring agent, water, a water-soluble organic solvent which is a liquid at least at temperatures of 40° C. or less, and which has a solubility of 1 wt % or greater with respect to water at a temperature of 20° C., and a saturation vapor pressure of 1.7 Pa or less at a temperature of 20° C. (with said organic solvent being contained in the ink composition at the rate of 10 to 35 wt %), and one or more amidine type compounds. As a result, the present invention provides an ink composition, a recording medium, recorded matter and an ink jet recording method that make it possible to obtain images with a high image quality which are superior in terms of the gas resistance of the recorded matter.