Calcining magnesite slag to capture CO 2 is a new and simple method of processing CO 2 and magnesite slag simultaneously. In this work, the CO 2 capture capacity by calcined magnesite slag in wet flue gas simulated by adding water vapour was investigated. The magnesite slag exhibits excellent CO 2 adsorption performance, with 3.01 mmol/g CO 2 adsorption capacity, which is reduced to 2.18 mmol/g after 8 cycles and is obvious superior to magnesite. The structure and characterization of the magnesite slag are examined by XRF, FT-IR, TG-DSC, XRD, CO 2 -TPD and BET. It can be confirmed by X-ray fluorescence analysis that the key component of magnesite slag is MgSiO 3 and MgCO 3 . The results of this work indicate that the magnesite slag is an available adsorbent for CO 2 adsorption after calcination.