Studies were carried out to follow chronological changes in hydrate formation on a surface of cement pastes spread on a glass slide and cured at 21℃ and 35℃ . The cement pastes with or without deflocculant were composed of high alumina cement（HAC）, silica fume（SF）and water. Different hydrates were characterized by XRD and analyzed by EPMA during the final stages of hydration. The samples were solidified 5-7 hours after mixing with water, and at first C2AH8 or C4AH13 crystallized. CAH10 was detected 1 day after C2AH8 appeared only in the samples cured at 21℃. In all samples, C4AcH11 （c:CO2）, which was formed by carbonation of C4AH13, was detected 1 day after C4AH13 appeared. Except for the sample without defloccurant cured at 21℃, C2ASH8（stratlingite） crystallized in all other samples. The relationship between disappearance of C2AH8 and crystallization of C2ASH8 was studied for each sample. C3AH6 was detected only in the sample without defloccurant cured at 35℃ . After 2 to 3 weeks of curing and hydration, the HAC hydrates such as CAH10, C2AH8, C2ASH8, C4AH13, C4AcH11, C3AH6 had vanished, and calcite and gibbsite crystallized in all the samples. Vaterite（CaCO3:Cc）crystals started to form only after calcite（CaCO3:Cc）had appeared.

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