To provide an inter-structure sealing bag installed in the gap between structures and capable of easily and properly preventing water from leaking by a hydraulic pressure acting to the gap from the outside.

This inter-structure sealing bag comprises a tubular woven fabric having no joint in the circumferential direction and a filler port for filling a self-curing fluid. Water leakage by the hydraulic pressure acting to the gap from the outside is prevented by installing the sealing bag in the gap between the structures and filling the gap with the self-curing fluid.