A series of P-Ni-Mo/Al2O3 catalysts with varying phosphorus content, prepared by co-impregnation, was studied by infrared spectroscopy of nitric oxide adsorption on their reduced and sulfided form. It was found that small concentrations of phosphorus (1 to 3 wt.-% P2O5) increased reducibility and sulfidability of nickel and molybdenum. A red shift of the band of nitric oxide adsorbed on molybdenum is observed for sulfided samples with low phosphorus content compared to phosphorus free. In the samples with high phosphorus contents (above 4 wt.-% P2O5) reducibility and sulfidability of nickel and molybdenum decreases. A blue shift of the band of nitric oxide adsorbed on molybdenum is observed and three types of nickel species are found with different degree of reduction/sulfidation in the sulfided form of these samples.