The effects of acid attack to structure and surface properties of sepiolite from Nevada, USA were investigated by using H2SO4, HCl and HNO3 under different conditions. It was found that 0.5M HNO3 attacking sepiolite sample for 4h was the optimal condition to remove impurities of dolomite and calcite, raising the content of sepiolite from 60.7 to 93.0 wt.%. With the intensity of acid attack increasing, the structure of sepiolite was destroyed. In H2SO4 attack process, the hydrogen ions reacted with the hydroxyl groups of the sepiolite first, and then reacted with the Mg2+ cations. The formation of CaSO4 not only prevented the replacement reactions between H+ and Mg2+ ions but also promoted the water absorption of sepiolite. In HNO3 and HCl attack process, Mg2+ cations were replaced by H+ ions first for HNO3 and HCl acid treatment, and then reacted with the hydroxyl groups of the sepiolite.