The CO2 absorption kinetics of Li4SiO4, which attracted interest as CO2 absorbent, under P(CO2) of 1.0, 0.1 and 0.03 bar was evaluated using thermogravimetry at fixed temperatures between 460 degrees C and 600 degrees C. Reaction rate and saturated reaction ratio increased with increasing temperature and P(CO2). Under P(CO2) of 1.0 bar and 0.1 bar, reaction rate at initial period was enhanced by decreasing particle size and variation of reaction ratio by time could be successfully explained by using Jander model assuming Li+ diffusion process induced by difference of CO2 concentration as rate determining step. Under P(CO2) of 0.03 bar, Jander model assuming superficial reaction between CO2 gas and Li4SiO4 solid surface as rate determining step was more applicable, indicating change of rate determining step varied from diffusion process to superficial one by decreasing P(CO2) from 0.1 bar to 0.03 bar.