Pulverized Japanese bituminous coal (Taiheiyo coal) samples with diameter ranges of 38-75 mum and 180-250 mum were gasified with high-pressure steam in the presence of Ca-based CO2 sorbents. The experiments were carried out at 873 and 973 K and at holding times ranging from 0 to 120 min using a laboratory-scale fixed-bed reactor, and the solid-solid reaction between the Ca-based sorbents and the coal-included minerals during the steam gasification was investigated. Local scanning electron microscopy-energy-dispersive X-ray analysis of the solid residues obtained under different conditions showed that some constituents of the coal-included minerals, such as Si and Al, were contained in the sorbent particles. The solid-solid interaction between the Ca-based sorbents and coal-included minerals became significant at the higher temperature and at longer holding periods. This interaction will locally decrease the CO2 sorption ability of the sorbents. However, when a holding time of less than 10 min was employed, the solid-solid reaction between the minerals and the sorbents was suppressed, even at 973 K, because the rate of formation of inorganic compounds through solid-solid reaction was low. In this case, our target carbon conversion (about 50%) was attainable, owing to the devolatilization during the heating period. Our results indicate that the holding time of the feedstock in the reactor should be shortened to avoid deactivation of the Ca-based sorbents during high-pressure steam gasification.