The way of using red mud - a hazardous substance created from the producing of aluminum hydroxide in removing NO2 gas is perfectly suitable with sustainable development of society in the future. This study focuses on estimating the efficacy of two different materials on treating NO2 gas: pure red mud material (non-neutralised by seawater - RM1) and hydrotalcite material created from red mud with the participant of the seawater (Seawaterneutralised red mud - RM2). Experiments were made to survey the treating ability through various factors: concentrations of input NO2 gas, flow speed of NO2 gas pass through materials, mass of materials, temperature of material used in experiments and saturated time of materials have also been tested. The results showed that seawater-neutralised red mud and red mud material were potent in the NO2 adsorption. However, RM2 material had the higher treating ability of NO2 gas than RM1 about 5 %. The result showed that optimal conditions were determined at concentrations of input NO2 were 303–397 ppm, flow speed of NO2 gas pass through materials was 0.4L/min, 10 g mass of materials, temperature of material was 30 oC. The efficiency of treating NO2 gas of RM1 and RM2 are 89.50 % and 84.43 %, respectively. The results of this study showed that both seawater-neutralised red mud and red mud have the potential to remove NO2 gas.