The application of modern technologies (i.e. IGCC) is generally considered as the most appropriate for low rank coals exploitation for energy production. These could provide a clean fuel for electricity generation with reduced emissions. Therefore, the study of the char reactivity is an essential feature towards optimising fuel efficiency and for sizing gasifiers. The variations in the reactivity of chars during gasification are related with the inherent properties of the parent coal and the pre-treatment conditions, particularly temperature, residence time and atmosphere. In this work the reactivity of chars prepared from Greek lignite with CO2 was studied. Lignite samples were initially pyrolysed under N2 and/or H2 flow (700 – 1000°C and 2 – 120 min) and the produced chars were gasified under CO2. Gasification tests were performed non-isothermally in a TGA apparatus and isothermally in a fixed bed reactor. Gaseous products were collected in both stages and were analysed mainly for CH4 and CO. The pore structure development was analysed by N2 and CO2 adsorption at 77 K and 298 K respectively. The effects of pre-treatment temperature, residence time and atmosphere on the reactivity of the produced chars during CO2 gasification were studied.