In this paper, municipal solid waste (MSW), sewage sludge (SS), and rice straw (RS) were pyrolyzed under N-2 atmosphere and at 550 and 600 degrees C, and then the produced biochars were used for gasification in a CO2 atmosphere. The effects of pyrolysis temperature, gasification temperature, and CO2/C ratio on the product composition and yield were studied. The results were compared with those from coal char gasification. The CO2 gasification kinetics were determined under CO2 flow by thermogravimetric analysis (TGA). CO concentration in the syngas of the gasification experiments can be organized in the following order: MSW char > RS char > SS char > coal char. Considering the energy consumption and CO yield, the recommended gasification temperature for the biomass chars is 900 degrees C. The activation energies of CO2 gasification calculated from the TGA data based on the most fitted reaction models can be organized in the following order: coal char > RS char > SS char > MSW char, which is consistent with the experimental results. For higher syngas field and lower CO2/C ratio, MSW char is recommended as the best feedstock for in the combined pyrolysis-gasification process.