A packaging material for lithium ion cell is comprised of a laminate obtained by successively laminating, on one surface of a base material, an adhesive layer, an undercoat treated layer, an aluminum foil layer, a corrosion inhibition treatment layer, an adhesive resin layer and a sealant layer. The undercoat treated layer contains the following components (A), (B), and (C). A total amount of the components (B) and (C) is at 200 to 12000 parts by mass per 100 parts by mass of the component (A). (A) A crosslinked resin formed of a resin (A1) having two or more nitrogen-containing functional groups and a resin (A2) having a reactive functional group capable of reaction with the nitrogen-containing functional groups. (B) A rare earth element oxide. (C) Phosphoric acid or a phosphate salt.