Two samples of nanocrystalline MFI zeolite with silicon to aluminium (SAR) molar ratios of 75 and 125 were hydrothermally synthesized by our improved one step procedure in static conditions at 200 degrees C under autogeneous pressure. Another sample with SAR = 50 was also synthesized by the conventional hydrothermal synthesis method. The samples were subjected to alkali attack to study the effect of duration of alkali treatment, concentration of alkali and method of synthesis on the stability of zeolite structure. Loss of crystallinity and change in crystallite size were investigated using XRD and FTIR. Samples were also characterized by TGA, N-2 adsorption and SEM analyses. The extent of removal of silicon by alkali treatment for creation of mesopores with preservation of the zeolite structure has also been investigated. (C) 2011 Elsevier B.V. All rights reserved.