The hydration behavior at 25°C of highly reactive β-dicalcium silicate synthesized from hillebrandite (Ca2(SiO3)(OH)2) was studied over a period of 7 to 224 d using 29Si magic-angle spinning nuclear magnetic resonance (MAS NMR). The hydration product, C-S-H, contains Q2 and Q1 silicate tetrahedra, the chemical shifts of which are independent of the water/solid (w/s) ratio and curing time. Until the reaction is completed, the amounts of Q1 and Q2 formed are independent of the w/s ratio, being determined only by the degree of reaction. The ratio Q2/Q1 increases as the reaction progresses and as the curing time becomes longer. From the values of Q2/Q1, it appears that the hydrate is a mixture of dimers and short single-chain polymers. The Ca/Si ratio of the hydrate is high, taking values close to 2.0, but the Ca/Si ratio does not influence the Q2/Q1 ratio. It was also found that the NMR peak intensities allow quantitative assessment similar to XRD.