Abstract: The waterstop used to prevent passage or leakage of water through a construction joint of concrete is shaped of a plastic or rubber in the form of a continuous-length belt-like form and provided with a water-swellable rubbery layer on at least a portion, or, for example, along the peripheries of the belt-like form, side-by-side coming into contact with the concrete bodies to serve as a water-tight filling of the joint by being swollen with water. The water-swellable rubbery layer is protected temporarily prior to use with a coating film of an alkali-soluble polymeric material which can at least partially be dissolved away by the alkalinity of the water in the concrete joint. The peripheries of the plastic- or rubber-made belt-like form are preferably in a length-wise bulged form having a bore running therethrough to serve as a stress absorber when the water-swellable rubbery layer is swollen with water.