Abstract: A novel polyester type powder coating composition which includes a specific self-hardening polyester of air-hardening type comprising as main ester-constituting monomer units, (1) at least one polycarboxylic acid component containing at least 10 mole %, based on the polycarboxylic acid component, of at least one aromatic polycarboxylic acid component (A) and (2) at least one polyhydric alcohol component, having in its main chain at least one terminal blocked with a monofunctional unsaturated alicyclic compound component (B) and having a softening point of 30.degree. to 150.degree. C. This composition is excellent in storage stability and adaptability to either thin coating or thick coating, and when it is applied onto an article to be coated and baked at a temperature of 170.degree. to 230.degree. C. for 5 to 30 minutes, a coating excellent in appearance, mechanical strength, gloss and reflection sharpness can be formed advantageously without generating undesired gases at the baking.

Abstract: A polyester obtained from dibasic acids mixture containing 10 to 50 mole-% of endomethylene-tetrahydrophthalic acid and glycols is used in a resin composition for powder coatings. This composition has a good storage stability and when heated in the air at 150.degree. to 220.degree.C exhibits favorable fluidity to form an even coating which quickly hardens to a film with excellent characteristics.