The morphology of early hydrates of a cement clinker was studied by SEM and EDS. The hydrates were formed on thin plates cut from the clinker and immersed in a solution containing Ca(OH)2, CaSO4·2H20, and varying amounts of sucrose and KOH. The results show the different influences of sucrose and of KOH on the formation of the hydrates, in particular on the crystallization of AFt. The sucrose plays a leading role, and altered the time of primary formation of AFt and its morphology. KOH did not. In CaSO4·2H20 saturated solution without sucrose, regardless of the presence or absence of Ca(OH)2, the foil -like hydrates, CxAHy are formed as the first result of reaction of C3A with water. Then CxAHy reacts with CaSO4·2H20 to form AFt. However, in the presence of sucrose the C3A reacts directly with CaSO4·2H20 to form AFt. It is supposed that sucrose acts as a catalyst for the formation of AFt crystals. During the early stage of cement hydration, AFt crystals appear to form by both topochemical and by through-solution reaction mechanisms.