The hydration kinetics of tricalcium silicate (Ca3SiO5) has been studied by time-of-flight neutron powder diffraction (TOF-NPD) and time-of-flight small-angle neutron scattering (TOF-SANS). During the hydration process, the hydrated Ca3SiO5 was quantified using the additional standard method with Si, and then we could obtain the time dependence of the hydration degree of Ca3SiO5. It was validated that the hydration of Ca3SiO5 proceeds in three different stages: induction period, nucleation and growth period and diffusion-limited period. In the SANS experiments, the drastic variation in the SANS curve was observed over induction time (t(i)similar to 6 h). From these results, we point out that the hydration rate is strongly associated with the surface roughness of Ca3SiO5 arising from the creation of hydration products. Furthermore, the four-parameter equation based on the Avrami model was applied to describe the hydration kinetics of Ca3SiO5. The n-value that characterizes the hydration process was estimated as similar to 2.6.