SO2 concentrations in oxy-fuel combustion flue gases increases about three times as high as that of conventional air combustion system owing to the flue gas recirculation for the control of combustion temperature. So the desulfurization reaction is different from that of the conventional air combustion system due to exceptionally high CO2 and SO2 concentration. In this study, drop tube furnace(DTF) system was used to investigate the desulfurization characteristics of limestone in oxy-fuel combustion furnace. The experiments were performed under O2/CO2 atmosphere to examine the effect of operating variables such as reaction temperatures, Ca/S ratios and inlet SO2 concentrations on the SO2 removal efficiencies. SO2 removal efficiency increased with reaction temperature, Ca/S ratio and inlet SO2 concentration. And the addition of water vapor resulted in about 4~6% of increase in SO2 removal efficiency.