The present invention relates to a plastic film (10) formed by a co-extrusion method, and an infusion bag formed thereof. The plastic film (10) includes at least three layers having: a first layer (1) constituted by a polyamide obtained by a ring-opening polymerization of a lactam having 11 or more carbon atoms or by polycondensing of an ω-amino acid having 11 or more carbon atoms, or a polyamide obtained by copolycondensing a dicarboxylic acid having 10 or more carbon atoms and a diamine having 6 or more carbon atoms; a second layer (2) containing a copolymer of an α-olefin and an anhydride monomer of an unsaturated carboxylic acid or an unsaturated dicarboxylic acid as the major component; and a sealing layer (3) containing a polyethylene as the major component.