An electrical measurement technique was used to measure the electrical resistivity of cement paste having varying water/cement (w/c) ratios, and consequently the paste properties and characteristics were analyzed. The different hydration periods were identified from the electrical resistivity curve and the differential electrical resistivity curve. The setting time for the samples is reached before the first peak of the differential electrical resistivity curve, and this can provide a new method to determine setting time by using electrical resistivity measurements. The relation between w/c ratio and bulk resistivity at a fixed curing time follows a power law, so electrical resistivity can be used for determination of the w/c ratio in fresh and hardened cement pastes after calibration. © 2006 ASCE.