The hydration behavior at 25°C of β‐dicalcium silicate synthesized from hillebrandite (Ca2,(SiO3)(OH)2) at 600°C was studied over a period of 224 d. The hydration rate of the β‐dicalcium silicate having fibrous crystals with specific surface area of 7 m2/g is extremely rapid. For water/solids ratios of 0.5 and 1.0, the hydration reaction is completed in 28 and 14 d, respectively. The hydrate contains almost no Ca(OH)2, and its Ca/Si ratio is close to 2. SEM observations indicate that the hydrate forms an outer shell on the surface of β‐dicalcium silicate and grows inwards. The silicate anion structure is considered to consist of dimers and single‐chain structures from29Si MAS NMR. Variations of physical properties of press‐formed bodies have also