A new method for the synthesis of nanosized zeolites in organic solvents, such as formamide and toluene as crystallization medium instead of water, in the presence of organosilane has been developed. Organic solvents have a great impact on the synthesis of nanozeolites. Formamide, which has similar properties to water, is a good candidate as the solvent for the synthesis of nanosized zeolites. This synthetic method allows easy manipulation with the control of crystal sizes. In this study, different crystal sizes such as 25, 40 and 100 nm were prepared in toluene and formamide solvents. To study the effect of crystal nanosizes on the catalytic performance of nanosized zeolites, nanozeolite-based FCC catalysts were also prepared using different nanozeolite sizes as active component and silica as inactive matrix. The activity of these catalysts was evaluated with FCC feedstock. The results revealed a good correlation between the crystal size of zeolites and the activity: smaller nanozeolite-based FCC catalyst exhibits higher catalytic activity. (c) 2010 Elsevier B.V. All rights reserved.