Disclosed is a coating material for forming a gas-barrier layer. The coating material contains a polyalcohol polymer, a polycarboxylic acid polymer, and a divalent or higher-valent metal compound whose surface is coated with a poorly water-soluble component, or alternatively a monovalent metal compound whose surface is coated with a poorly water-soluble component and a divalent or higher-valent metal compound. By applying this coating material over a plastic base layer, there can be obtained a gas-barrier multilayer body having a gas-barrier layer.