Binary lignite blends were prepared using two high mineral matter Turkish lignites from Soma and Afsin-Elbistan regions and their burnouts were investigated up to 900 degrees C by thermogravimetric analysis and differential thermal analysis methods. Blending ratios were in the range of 5-25 wt-% in which Afsin-Elbistan lignite was the major component. Mass losses during co-combustion were considered to interpret the thermal reactivity and the burnout characteristics of the blends according to synergistic approach. It was concluded that co-combustion of the lignite blends led to significant increases in the burnout yields almost at any temperature. Besides, increasing blending ratios changed the behaviour of blends from additive behaviour to the synergistic interaction. Especially, blending ratio of 15 wt-% showed important deviations from the expected values in terms of burnouts, maximum burning rate and differential thermal analysis peak temperature.