An exterior material for a lithium ion battery, which comprises a base material layer, and also comprises an adhesive agent layer, an aluminum foil layer provided with a anti-corrosion-treated layer and an adhesive resin layer which are laminated on one surface of the base material layer in this order, wherein the adhesive resin layer comprises an acid-modified polyolefin resin and a compatible elastomer which is dispersed in the acid-modified polyolefin resin at a dispersion phase size of not less than 1 nm and less than 1 [mu]m.