The properties of a bi-functional catalyst based on a new amorphous mesoporous silica-alumina (MSA) exhibiting a very narrow pore size distribution has been studied for the n-decane hydroisomerization-hydrocracking reaction. The hydrogenation-dehydrogenation function has been provided by supporting platinum on the MSA surface. The amount and the dispersion of platinum in Pt/MSA catalysts were optimized to provide pure bi-functional behavior. The activity of final catalysts was compared with that of a commercial silica-alumina (Crossfield) and three USY zeolites (PQ Corp.) having different framework Si/Al ratios. The observed differences have been discussed and hypothesis based on differences in acid properties and porosity have been proposed in this paper, A study of the product distribution based on different criteria used in the n-decane reaction test allowed to exclude the presence of ZSM-5 domains in the structure of the precursor MSA mesoporous material.