There is provided a printing ink to be used in the production of a heat insulating foamed paper container obtained by heating a paper container which has a container body unit laminated with a high-melting point thermoplastic synthetic resin film on the inner surface and with a low-melting point thermoplastic synthetic resin film (low-Mp resin film) on the outer surface, and thereby foaming the low-Mp resin film, the printing ink being printed on the laminated low-Mp resin film upon the production of the paper container but inhibiting the occurrence of differences in level at the foamed surface of the low-Mp resin film. In an ink composition for printing on foamed paper containers, which contains a colorant, a binder resin and a solvent, a resin having an elongation ratio (elongation ratio as measured with a small-size tensile tester manufactured by Intesco Co., Ltd., under the conditions of a tensile speed of 100 mm/min and room temperature (25° C.)) of 400% to 3,000% is used as the binder resin. The binder resin is preferably a mixture of a urethane resin:vinyl chloride/vinyl acetate copolymer (=50:50 to 99:1), and the urethane resin is more preferably a polyurethane-urea resin. A non-aromatic solvent is used as the solvent.