The dielectric constant, epsilon, and electrical conductivity, sigma, of mortars with various sand-cement ratios, s/c, were measured for the first 30 h hydration using microwave techniques in the frequency range 8.2-12.4 GHz. The epsilon and sigma of the mortars were found to increase linearly with increasing water-solid ratio w/(s + c), but decrease with increasing s/c. It was found that as long as the sie values were the same, the rate of changes in epsilon and sigma of the mortars were the same. It appears that the s/c is the key factor controlling the rates of changes in dielectric and electrical parameters of cement hydration in mortar. The relationship between compressive strength and dielectric and electrical properties of mortars was also discussed.