Reactivities of three chars with CO 2 and steam were examined using a Thermogravimetric Analyzer (TGA). Similarities and differences between kinetics of char–CO 2 gasification and char–steam gasification have been discussed. As a result, for both reactions, the measured gasification rate increases with temperature and decreases as the particle size increases. And the initial rate of char–steam gasification is always several times faster than that of char–CO 2 gasification. Moreover, for the char with lower reactivity, the activity of its steam gasification reaction possesses larger difference with that of CO 2 reaction. An nth-order model with the effectiveness factor was used and a characteristic parameter (Tc, which is the temperature in the case of Thiele modulus ϕ=3.) was proposed to compare the difference between the pore diffusion effect on steam gasification and CO 2 gasification. The results show that the pore diffusion resistance increases with the gasification temperature and particle size. However, for each sample, Tc of char–steam gasification is always lower than that of char–CO 2 gasification. The pore diffusion effect on char–steam gasification is more significant than that on char–CO 2 gasification. Moreover, the difference between the pore diffusion effect on char–steam gasification and char–CO 2 gasification is larger for the char with lower reactivity.