The effect of the presence of steam and SO2 on CO2 sorption capacity during multicycle carbonation-calcination tests on three limestone types from Germany, Greece, and Poland was studied. The behavior of carbonation conversion under realistic process atmospheres containing SO2 and additionally steam as well as of sulfation under similar temperature conditions was investigated. The deactivation effect of SO2 on CO2 sorption capacity in two cases with and without steam was analyzed. The negative impact of the competitive sulfation reaction towards carbonation increased in the subsequent cycles for both cases, but to a less extent in the presence of steam. Sulfation conversion changed quite monotonically in the subsequent cycle in dry gas, whereas in the presence of steam sulfation conversion decreased slightly while carbonation conversion increased. It was found for the tested sorbents that carbonation conversion decreased to varying degrees in the presence of SO2. The Polish and Greek limestone showed the largest loss of sorption capacity in the presence of SO2. The quantitative influence of SO2 on carbonation conversion in dry and wet gas was determined.