Three series of mesoporous aluminosilicate molecular sieves, MCM-4l, with various Si/A1 ratios were synthesized using different aluminum sources (aluminum isopropoxide, pseudo boehmite and aluminum sulfate). XRD analysis, temperature programmed desorption of n-butylamine, Al-27 and Si-29 MAS NMR, and catalytic alkylation test indicated that aluminum isopropoxide is a better source for incorporating aluminum in the framework of MCM-41 type molecular sieves with better crystallinity and acid characteristics.