To provide a biaxially oriented polyester film which is excellent in gas barrier properties such as an oxygen gas barrier property, mechanical characteristics such as elastic modulus, gloss, printability, methylation, coatability, and winding characteristics, and at least whose one side has an excellent adhesion-promoting property for adhesiveness to other polymers, metals, and printing inks.

This biaxially oriented polyester film comprising a polyester and poly(m-xyleneadipamide) is characterized in that the elastic moduli of the polyester film are ≥3500 Nmm2 in the longitudinal direction and in the lateral direction, respectively, and at least one side of the polyester film has an adhesion-promoting property.