To provide a method for monitoring solidification of water granulated blast-furnace slag so as to effectively use the slag, by measuring a progression degree of solidification of the water granulated blast-furnace slag, and a device therefor.

The method for monitoring the solidification of the water granulated blast-furnace slag is characterized by grasping a solidification state of grains of the water granulated blast-furnace slag, on the basis of variation in an electric capacity or an electric conductivity of the water granulated blast- furnace slag with time. The device for monitoring the solidification of the water granulated blast-furnace slag comprises a pair of electrodes for applying an electric field on the grains of the water granulated blast-furnace slag, and instruments which can measure the electric power capacity or electric conductivity between the electrodes.