The NiMo(W) and PNiMo(W) catalysts supported on carbon obtained from peach stones were studied. The catalysts were prepared using two different impregnation techniques: pore filling and excess of solution. Impregnating solutions of molybdenum or tungsten iso-and heteropolyanions were used as precursors of the active components. The textural properties of the catalysts were determined, and also they were characterized by Fourier transform infrared spectroscopy, temperature programmed reduction and scanning electron microscopy. Their surface acidity and their hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activities were measured. The positive influence of phosphorus on HDS and HDN activity of both molybdenum and tungsten-based catalysts was confirmed. It was found that the HDN activity depends strongly on the preparation method and on the W and Mo precursors used in the impregnating solution. The PNiMo and PNiW catalysts on carbon prepared by impregnation with heteropolyanions solutions were as or more active for HDN reaction than those obtained from the classical isopolyanions. © 1999 Elsevier Science B.V. All rights reserved.