Arsenic emission during fuel combustion is of great concern due to its high toxicity. CaO shows a great capacity for arsenic capture and the addition of CaO is a promising way to suppress arsenic emission during fuel combustion. SO2 in the flue gas could also react with CaO and might influence arsenic capture. It remains unknown which temperature is proper for CaO injection for arsenic capture considering the effect of SO2. And the reaction mechanism is still unclear at different temperature range. In the present study, the capture of arsenic by CaO was investigated in simulated flue gas with and without SO2 at temperatures ranging from 573 to 1323 K. The results show that arsenic capture was predominantly through physical adsorption at 573 and 723 K while was mainly carried out through chemical oxidation at higher temperatures. With temperature increasing, arsenic capture was enhanced. Nevertheless, the sintering of CaO particles occurred at 1173 and 1323 K. It is sure that arsenic capture was remarkably suppressed at these temperatures owing to the particles sintering. On the other hand, SO2 competed with arsenic vapors to react with CaO. The enhancement of sulfate reaction strongly inhibited arsenic capture with temperature increased from 573 to 1023 K. At higher temperatures, the formed CaSO4 was confirmed to be able to absorb arsenic vapors which could partly facilitate arsenic capture. Considering the sintering of CaO particles and the effect of SO2, the proper temperature for arsenic capture should be around 873 K. (C) 2015 Elsevier B.V. All rights reserved.