A new type leakage isolation sheet with self-repairing mechanism is presented, in which there is no water leakage when the sheet is broken. The sheet consists of two rubber sheets with lattices inside. Polymer particles are in the lattices, and sandwiched between the rubber sheets. The polymer particles expand in contact with water, and they become gel. The large pressure is generated in the lattice of the sheet. Hence, the sheets isolate water leakage. When the rubber is broken, polymer particles fall down with water. In order to keep the particles in the lattice of the sheet, textile sheets lie on the back surfaces of the rubber sheets. Experimental tests have carried out for a model of the sheet, and it is clarified that the proposed sheet isolates leakage perfectly under 1 MPa pressure when the sheet is broken by 10 mm diameter punch.