In a packaging body provided with at least an inner layer composed of a thermal-adhesive polyolefin based resin and a barrier layer composed of a metal foil, in which metal terminals are sealed by the thermal-adhesive resin with unconnected ends of the metal terminals protruding outside, an adhesive sheet for sealing metal terminals of a flat electrochemical cell which is not only able to prevent a short circuit between the barrier layer and the metal terminals but high in a layer-to-layer adhesive strength and a low possibility of a reduction in battery performance to be caused due to invasion of moisture is provided. In the adhesive sheet for sealing a metal terminal part of a flat electrochemical cell according to the invention, a fibrous sheet or a porous sheet is covered by the inner layer and an acid-modified polyolefin based resin layer having adhesive properties.