To provide such a water-proof sheet for a corner as being capable of accommodating oneself to a plurality of different gradients, reducing its manufacturing cost and performing proper construction.

A water-proof sheet 1 for a corner mounted at the reentrant angle of a building, exposed to the outside, is formed with a plane bottom 2 and two sides 3a, 3b crossing each other. A cutout 5 is formed in one side 3a along and near a vertical ridge line 4, where both sides 3a, 3b cross each other. A folded sheet 6 in almost sector form, easy to bend, large enough to block the cutout 5, when the other side 36 is inclined outward at the maximum for the cutout 5 to be enlarged, is adhered to the overlap width at the peripheral edge of the cutout 5.