A series of solid-acid catalysts comprised of gamma-alumina and modified gamma-alumina with different of silica were prepared by co-precipitation method. The catalysts were characterized using XRD, TGA, NH3-TPD and BET techniques. Dehydration of methanol to dimethyl ether (DME) on solid-acid catalysts was studied in a fixed-bed reactor at the same operating conditions (T = 300 degrees C. P = 16 bar, WHSV = 26.07 h(-1)). According to the experimental results, silica-modified catalysts have shown better performance compared to the pure gamma-alumina. It was found that surface areas increase with increasing silica loading. The results of NH3-TPD analysis showed that the surface acidity of aluminosilicate catalysts increases with increase in SiO2/Al2O3 molar ratio. Also, it was found that the catalysts with highest portion of weak and/or moderate acid sites exhibit the best catalytic performance and stability. The sample with 3 wt.% silica loading has exhibited the best activity for methanol conversion. (C) 2009 Elsevier B.V. All rights reserved.