Aluminosilicate mesoporous molecular sieves (designated Al-MMS) have been prepared at room temperature using the primary amine hexadecylamine as organic templating surfactant, The materials have textural properties typical of mesoporous materials with short-range hexagonal order but exhibit higher Bronsted acidity compared to aluminium-containing MCM-41. The Pt-impregnated materials are efficient catalysts for the hydroconversion of n-heptane. At low Si/Al ratio (less than or equal to 10) the materials have total conversions and selectivity comparable to that of USY zeolite (Si/Al=21) and in addition exhibit considerable cyclisation at temperatures above 350 degrees C. Our catalytic results show that the Pt-impregnated Al-MMS samples attain a good balance between the metal and acidic functions and that activity and selectivity : are dependent on the Bronsted acid content and consequently on the amount of tetrahedral aluminium in the catalysts. The amount of Pt (in the range 0.25-1 wt%) mainly affects the selectivity to cyclised products which increases with Pt content at the expense of cracking; total conversion and selectivity to isomers remain largely unaffected.