Co-firing of coal with biomass suffers from high thermal reactivity of biomass. Thus, this paper discusses the effectiveness of carbonization to reduce the excess reactivity of biomass to avoid segregation of coal and biomass during co-firing. In this context, Robinia pseudoacacia (RP) that is a promising woody biomass has been subjected to carbonization at 600 degrees C to obtain a biochar that has relatively lower reactivity. Fuel properties and thermal analysis profiles (TGA, DTG, DSC) of biochar were compared with those of biomass and lignite to valorize the effectiveness of carbonization. Segregation of biomass and lignite during co-combustion before and after carbonization was investigated considering 50/50 wt% blends. It was concluded that carbonization based co-firing of biomass with lignite mostly eliminates segregation tendency in the mass loss characteristics as well as the heat flow pattern due to the change in the burning mechanism that leads overlapping the temperatures of maximum rate of weight loss (TR-max) and maximum heat flows (TH-max). The carbonization process allows co-utilization with high substitution ratios of biomass. Carbonization based co-firing of biomass and lignite also showed that the heat flow pattern does not suit to additive behavior, while the weight loss characteristics are partly additive and partly non-additive depending on the temperature interval. (C) 2015 Elsevier B.V. All rights reserved.