To obtain a water stop material applicable to a vertical surface, simply applicable even to a complicated shape and exhibiting sufficient water stop effects and to provide a method for stopping water among sheetlike or platy waterproof materials using the water stop material.

This water stop material comprises an unvalcanized rubber composition consisting essentially of an unvalcinized rubber and having ≥100°C heat-resistant flow. The method for stopping water comprises joining superimposed parts among the sheetlike or platy waterproof materials using the water stop material.