[Problem] To provide a hydroxyl group-containing polyester resin composition that exhibits high gas barrier performance through the effect of high cohesive energy due to hydrogen bonding of the polyester resin itself even without using a large amount of isocyanate curing agent and can be used as a flexible adhesive, and a coating film and a packaging film formed therefrom. [Solution] A resin composition that contains a hydroxyl group-containing polyester resin and satisfies (1)-(2) below.　(1) The composition contains a polycarboxylic acid component and a polyhydric alcohol component as constituent components of the hydroxyl group-containing polyester resin and contains 10 mol% or more of a polycarboxylic acid component having a hydroxyl group when the total amount of polycarboxylic acid component is taken to be 100 mol%. (2) The composition contains 0.1-15 mass parts or more of isocyanate curing agent per 100 mass parts of hydroxyl group-containing polyester resin.