The effects of boron on the dispersion of active metal species and hydrodesulfurization (HDS) activity of dibenzothiophene (DBT) over Ni-Mo/gamma-Al2O3 containing boron were studied by means of BET surface area measurement, powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Mo K-edge extended X-ray absorption fine structure (EXAFS), and B K-edge X-ray absorption near-edge structure. The HDS activity of DBT over Ni-Mo/gamma-Al2O3-B2O3 reaches a maximum at the B2O3 loading of about 1 mol%, in agreement with the basal dispersion and thus with the hydrogenation ability of the catalysts. It has been proven that the combination of XRD, XPS, and EXAFS techniques gives a complete description of the dispersion of active metal species in heterogeneous environmental catalysts.