There is provided a primer composition capable of effectively enhancing anti-plasticizer property and water resistance even without curing of the primer layer, and a bonded structure. A primer composition forms a primer layer, containing a polymer, of a paint film formed by painting and drying on a surface to be painted; and a bonded structure includes: a base material, a primer layer containing a polymer sticking fast to the base material, and an adhesive sheet having an adhesive layer stuck fast to the primer layer. The polymer contains a polycarbonate polyurethane having a repeated unit derived from polycarbonate polyol in a molecule thereof.