Abstract: Provided is a polyester-based sealant film having highly excellent heat seal strength and excellent recyclability. A polyester-based sealant film of a first aspect of the present invention is a laminated film composed of at least two layers and having a sealing layer and an outermost layer, in which the sealing layer includes a copolymerized polyester formed from a copolymer of terephthalic acid as well as another dicarboxylic acid component and a diol component, the outermost layer includes homopolyethylene terephthalate as a main component, the laminated film has a lamination configuration in which a content proportion (mol %) of the other dicarboxylic acid component in each layer decreases from the sealing layer toward the outermost layer, and a heat seal strength obtainable when the sealing layers of the laminated films are sealed at 0.2 MPa for 1 second in the range of 140° C. to 220° C. is 25 N/15 mm or higher.