Gaseous ozone (O 3 ) in the troposphere is considered to be one of the most harmful air pollutants in view of its high reactivity and immediate action to the surroundings, which causes both short-and long-term adverse health effect and also disrupts plant growth. [1][2][3] Materials explored for eliminating O 3 in several applications include activated carbon or carbon-promoted oxide materials, noble-metal-supported catalysts, and various transition-metal oxides. [3][4][5][6] These materials have diverse drawbacks: they must often be deposited on high-surface-area metal oxides or mixed with organic additives to enhance their performance, they use expensive metal components, they are not very environmentally friendly, and they are not flexible enough to use as a common choice in a wide range of sectors. Herein, we report for the first time that the two-line ferrihydrite (2LFh) with accessible mesopores can be used as a potential candidate for O 3 removal. The following aspects prompted us to consider mesoporous 2LFh (M2LFh) a judicial choice for O 3 removal: 1) it possesses high surface area and, being in the ferrihydrite (Fh) phase, a much higher percentage of iron sites are at or near the surface than in the bulk; [7][8][9] 2) with accessible mesopores, Fh nanoparticles have the potential for high adsorption owing to an increased rate of mass transfer to the reactive iron sites, such as we recently reported for their high efficiency in rapidly removing organic contaminants in the air;[10] and 3) as an oxyhydroxide of iron, Fh is environmentally friendly and can be applied in various sectors. We also show herein that the presence of Fh nanoparticles in disordered mesostructured iron oxide has a significant effect on the bulk and surface structure of the material and on the activity. Our findings can contribute toward designing Fh-based materials as new potential catalysts for rapid removal of O 3 and its decomposition.M2LFh was prepared according to a reported procedure [10] by assembly of Fh nanoparticles in 1-propanol in the presence of polyoxyethylene (20) cetyl ether template. Additionally, a mesostructured semicrystalline iron oxide composed of amorphous Fh nanoparticles and crystalline g-Fe 2 O 3 phase (MSIO) and a crystalline iron oxide with no welldefined mesopores (CIO) were prepared for comparison. MSIO was prepared through a sol-gel process in which iron nitrate, oleic acid, a triblock polymer template (F127), and 1-propanol were mixed, with subsequent ageing and calcination. CIO was prepared by assembly of iron oxyhydroxide in a water/ethylene glycol mixture in the presence of cetyltrimethylammonium bromide. Details of MSIO and CIO synthesis are given in the Supporting Information.The wide-angle XRD pattern of M2LFh (Figure 1 a,A) shows two broad reflections of the 2LFh phase. Although the amorphous Fh-phase reflections in the XRD pattern of MSIO (Figure 1 a,B) were disguised to a great extent by the crystalline peaks of g-Fe 2 O 3 , the analysis of the Mössbauer spectrum (see Table S1 in the Support...