In this work Pt catalysts (1 wt. %) were prepared by incipient wetness impregnation employing a series of mesoporous Al-modified MCM-41 at Al₂O₃/SiO₂ mass ratios equal to 10, 25 y 40 by means of chemical grafting method. Such materials were characterized and tested in the HDS of dibenzothiophene (DBT) and 4,6 dimethyldibenzothiophene (4,6-DMDBT) as model molecules in a batch reactor to similar industrial conditions (320 °C and 5.5 MPa). These Pt catalysts exhibited higher activity than Pt/Al₂O₃ used as a reference. The order of activities was: Pt/Al(40)MCM41 > Pt/Al(10)MCM41 ≈ Pt/Al(25)MCM41 > Pt/Al₂O₃ >> Pt/MCM41and selectivity was mainly to desulfurization products. The most active catalyst was tested in the HDS of 4,6-DMDBT and the results showed an important effect for Al in the HDS of highly refractory molecules.