A novel mesoporous SiO2 material (M-SiO2) with MCM-41 structure was readily fabricated from the inexpensive coal gangue via a hydrothermal reaction in the presence of cetyltrimethylammonium bromide (CTAB) for CO2 capture. On the basis of orthogonal experimental results, the optimum conditions for the preparation of M-SiO2 were identified as follows: the SiO32- leaching of 21 g/L from coal gangue, the CTAB concentration of 0.25 mol/L, the HCl concentration of 2.5 mol/L, the hydrothermal temperature of 393.15 K, and the hydrothermal time of 20 h. Under the optimum condition, the M-SiO2 exhibited an adsorption capability of 9.61 mg/g to 8% CO2 at 298.15 K. To further improve the CO2 adsorption performance, the M-SiO2 was chemically modified using ethylenediamine (EDA), and the optimum conditions for the modification of M-SiO2 were identified as follows: the impregnation time of 10 h, the drying temperature of 343.15 K, and the ratio of EDA/M-SiO2 = 2:1. Under the optimum conditions, the adsorption capability of EDA-modified M-SiO2 (EDA-M-SiO2) was increased by 83.5 mg/g. The obtained M-SiO2 and EDA-M-SiO2 were systemically characterized by N-2 adsorption-desorption isotherms, thermogravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction measurements techniques. The analytical results indicated that the M-SiO2 was mainly composed of O and Si in the form of SiO2 with a specific surface area of 156 m(2)/g, and part of M-SiO2 exhibited a structure similar to MCM-41. Moreover, the mechanisms of EDA modification and CO2 adsorption were investigated and discussed in detail.