Alumina support with a multimodal pore system was synthesized using a sol-gel method and modified with different amounts of phosphorus (0, 1.5, 1.7, 3.2 wt.% P); from these supports, catalysts containing 18 wt.% Mo were prepared. Catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and nitrogen physisorption, and tested in the hydrotreatment of Maya crude. For comparison purposes, hydrotreatment experiments were also performed without catalyst and with the P-modified and unmodified alumina support. The gas phase was analyzed by gas chromatography ( GC) and the asphaltene content was quantified in both, liquid and sediment. The distribution of the liquid fractions was obtained by thermogravimetric analysis. The results indicate that phosphorous addition causes a decrease in molybdenum dispersion and, when added in small amounts, an increase in the transformation of asphaltenes to valuable liquids. For the catalysts MoS2/Al2O-(1.5 wt.% P) was observed a decrease in asphaltenes transformation; however this catalysts generates less coke precursors and lead to an improved liquid yield. The behavior was due in part to the medium strength acidity of the P-modified alumina support and the increased hydrogenation function of the catalyst. (C) 2013 Elsevier B.V. All rights reserved.