Carbonatable calcium silicate cementitious material is a novel low-carbon building material with a great potential for development. γ-dicalcium silicate is one of the most carbonation reactive minerals among calcium silicates. In this paper, a wet powder of γ-dicalcium silicate was used as an experimental material. The influences of reaction duration, particle size, relative humidity, temperature, partial pressure and water-to-solid ratio on the degree of carbonation were investigated. The carbonation kinetic equation was proposed based on the modified shrinking-core model and empirical equation. It is indicated that the data predicted by the kinetic model are in reasonable agreement with the experimental results. The obstruction of ions diffusion attributed to the coating of carbonation products is a major factor of controlling the carbonation reaction.