CaO was added to lignite (S content 0.62% by mass) combusted in a lab. pilot plant with circulating fluidized bed (thermal capacity 0.1 MW) to compare its efficiency in flue gas desulfurization with limestone. The sorbents were fed in the combustion chamber directly with the fuel (mol. Ca/S ratios 2, 3 and 4). The addn. of CaO resulted in Increase in desulfurization efficiency by 11% when compared with the use of limestone.