The so-called micro fluidized bed reaction analyzer (MFBRA) was adopted to implement the isothermal gasification of in situ coal char with CO2 under minimized external diffusion inhibition. It was done by keeping the reaction atmosphere and temperature in the MFBRA for both coal pyrolysis and char gasification. This was further compared to the gasification of two other kinds of ex situ chars. While the gasification of ex situ char 1 referred to the coal pyrolysis in Ar and then CO2 gasification of the resulting hot char without thermal annealing (cooling) in the same MFBRA, that of the ex situ char 2 was by first a separate coal pyrolysis in Ar and then gasification of the char in the MFBRA after thermal annealing (cooling). Reaction characterization and kinetic parameters based on the measured time-series product gas composition of CO clarified that the in situ coal char had the highest gasification reactivity and the lowest activation energy, whereas the ex situ coal char 2 showed the lowest gasification reactivity and the highest activation energy. Comparing the gasification behavior of chars made with Yima (YM) bituminous coal and Xilinhaote (XLHT) lignite further demonstrated that the char of XLHT lignite had the higher reactivity and smaller activation energy, complying with the higher gasification activity of lignite char than that of bituminite char.