Mesoporous molecular sieves, MCM-41, were synthesized from sepiolite using acid leaching, followed by hydrothermal reconstruction and then calcinations at 540 degrees C for 5 h. The structures and the porosity of MCM-41 were investigated by means of small-angle X-ray diffraction patterns, Brunaer-Emmett-Teller (BET), Si-29 MAS NMR, Fourier transform infrared (FTIR), and high resolution transmission electron microscope (HRTEM) methods. The results showed that the hexagonal MCM-41 was formed in an alkaline solution of pH 12, when crystallization was carried out at 100 degrees C for 24 h. The specific surface area, pore diameter, and pore volumes of MCM-41 from sepiolite were 1036 m(2)/g, 2.98 nm, and 1.06 cm(3)/g, respectively. Si-29 MAS NMR results revealed that amorphous silica decomposed into Si-O chains consisting of two layers of Si atoms, with Q(3) configurations resulting in an increase in the fraction of Q(3) configuration during the crystallization of post-Mg-extraction sepiolite. The IR results illustrated that the complex of equivalent to equivalent to SiO--CTA(+) was formed during the synthesis of MCM-41 from post-Mg-extraction sepiolite.