This coating solution for a gas barrier contains an ammonium salt of a polymer having a carboxyl group (A), a particulate multivalent metallic compound (B), and water, the content of the multivalent metallic compound (B) being 0.5-2.0 times the chemical equivalent of the ammonium salt (A), and the mean particle diameter of the multivalent metallic compound (B) being 4 µm or less.