Several materials are used to design the sorbents applied in a fast-fluidized bed process for post-combustion CO2 capture. In this study, K2CO3-based dry sorbent (KMC) was prepared by using Micro-cell C (MCC), one of the materials used to design the sorbent, and then its CO2 sorption and regeneration properties were evaluated. KMC sorbent showed a low CO2 capture capacity of 21.6 mg CO2/g sorbent, which is about 22% of the theoretical value (95.4 mg CO2/g sorbent) even at 1 cycle, and showed a low CO2 capture capacity of 13.7 mg CO2/g sorbent at 5 cycles. It was confirmed that the KMC sorbent was deactivated due to the formation of a K2Ca (CO3)2 phase, resulting from the reaction of the K2CO3 with the Ca component contained in the MCC. In order to solve the deactivation of sorbent, and KM8 sorbent was prepared by adding the process of calcining the MCC at 850 °C. The KM8 sorbent showed a high CO2 capture capacity of 95.2 mg CO2/g sorbent and excellent regeneration property. Thus, it was confirmed that the deactivation of the sorbent could be solved by adding the calcining step to remove the side reaction causing material.