The aim of the present work is to study the effect of active belite on the hydration of C4A3S̅ and C4AS̅. The results revealed that the active β-C2S prevents the formation of crystalline ettringite and monosulfate hydrate as detected from the results of XRD. On the other side, the sulfoaluminate hydrates such as AFt and AFm were detected by using DSC technique. Gismondine C4Al8Si8O32·16H is formed from the reaction of β-C2S or CSH with the liberated Al(OH)3 from the hydration of C4A3S̅. This phase was not detected with the other monosulfate mix C4AS̅. This is mainly due to the absence of AH3 during the hydration of C4AS̅. The results of XRD patterns are in good agreement with those obtained from DSC thermograms.