Abstract: The electrical resistivity of cements with additions of carbon fibers or carbon black (CACs) at different drying times and soaking times was measured by a directcurrent fourpole method. The influence of water content in the CACs on their electrical resistivity was studied. It was found that the electrical resistivity of the CACs decreases with drying time and increases with soaking time. The electrical resistivity of CACs is sensitive to the change of their inner water content and they have a good humidity sensing property.