C-S-H with different Ca/Si ratios, formed from the hydration and pozzolanic reactions of blended cement paste, are the major calcium-bearing phases which react with CO2 during the carbonation. Therefore, it’s important to study the carbonation rate of different C-S-H phases. In this paper, the C-S-H phases (Ca/Si ratio: 0.66 to 2.0) were synthesized and used for the accelerated carbonation test with the CO2 concentration of 3%±0.2. Synthesized C-S-H phases with different Ca/Si ratio were identified by 29Si nuclear magnetic resonance (NMR). Carbonation rate and products of different C-S-H phases were studied by NMR and Fouriertransform infrared spectroscopy (FTIR). The results show that C-S-H phases with different Ca/Si ratio (lower than 1.40) was synthesized. C-S-H with lower Ca/Si ratio is decomposed faster than that with a higher Ca/Si ratio. After three days’ accelerated carbonation, the C-S-H phases with different Ca/Si ratio were all fully decomposed to CaCO3 and silica gel.@en