The effects of sodium salt of naphthalene formaldehyde sulfonic acid and stearic acid on the hydration of silica fume and Ca（OH）2 have been investigated. The hydration was carried out at 60°C and W/S ratio of 4 for various time intervals namely, 1,3,7 and 28 days and in the presence of 0, 2% and 5% superplasticizer and stearic acid. The results of the hydration kinetics show that both admixtures accelerate the hydration reaction of silica fume and calcium hydroxide during the first 7 days. Whereas, after 28 days hydration there is no significant effect. Generally, most of free calcium hydroxide seems to be consumed after 28 days. In addition, the phase composition as well as the microstructure of the formed hydrates was examined by using X-ray diffraction analysis （XRD） and scanning electron microscopy （SEM） respectively.
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