To obtain a sealant film for a bag-in-box which has suitable flexibility and excellent formability, heat sealability and heat seal strength, is improved in creation of pinhole and impact strength and is free from odor of acetic acid.

This film is prepd. in the presence of a metallocene catalyst having a single polymn. activity site and comprises a mixed resin composed of 3 to 40wt.% linear low-density polyethylene (a) having a density of 0.850 to 0.900g/cm3 and a melt flow rate of 0.1 to 2.5g/10min and 97 to 60wt.% conventional linear low-density polyethylene (b) having a density of 0.900 to 0.925g/cm3 and a melt flow rate of 0.1 to 2.5g/10min. The film may have a three-layer structure of an intermediate layer, formed of the linear low-density polyethylene (a), interposed between outer layers formed of the conventional linear low- density polyethylene (b).