A packaging material for a power storage device, comprising at least: a substrate layer; a metallic foil layer with an anti-corrosion treatment layer being disposed on one face or both faces thereof; and a sealant layer in this order, wherein the sealant layer includes a polypropylene-based resin (A) and 1 to 40% by mass of incompatible component (B), and maximum seal strength SM in an adhered portion resulting from adhesion by heat-sealing the packaging material is 35 N/15 mm or more, and in addition, the packaging material for a power storage device satisfies the following requirements (1) or (2): (1) a ratio SS/SM of seal strength SS to maximum seal strength SM in a stable range is 0.3 or more; (2) a ratio SA/SM of average seal strength SA to maximum seal strength SM is 0.3 or more.