The present invention provides a polyester film suitable for use as a sealant, which not only has high heat sealing strength, but also is less liable to adsorb various organic compounds, and has a less shrinkage in heating and high tensile strength. Further, the present invention provides a laminate comprising at least one layer of the polyester film, and a packaging bag including the same. The polyester film which is formed with a polyester resin whose main constituent is ethylene terephthalate. The film has at least one heat sealing layer. The film has a predetermined heat sealing strength, a predetermined difference in reversing heat capacity measured with a temperature modulated DSC, and a predetermined heat shrinkage. Further, the laminate comprises at least one layer of the polyester film, and the packaging bag includes the same.