Quick EXAFS was employed to follow the sulfidation of Mo and Ni in SiO2-supported NiMo hydrotreating catalysts, prepared in the absence and in the presence of the chelating ligands nitrilotriacetic acid (NTA), ethylenediamine (EN), and ethylenediaminetetraacetic acid (EDTA). Their catalytic activity was tested by means of thiophene hydrodesulfurization at atmospheric pressure. The sulfidation of Mo in the oxidic form to MoS2 occurred via an oxysulfide product and an MoS3-like material. Ni was sulfided in a narrow temperature range, and no intermediate products were observed. The presence of the chelating agents affected Mo only for ligand:Ni ratios greater than 1. In all cases, the sequence of the sulfidation regions remained unchanged, but the sulfidation interval became wider at higher ligand concentrations. The effect of the ligands was more pronounced on Ni, the sulfidation temperature of which was drastically increased by the presence of NTA and EDTA and decreased by EN.