The characterization of various spent Ni(Co)MoP/Al(2)O(3) catalysts has been performed in order to elucidate the active phase modifications undergone on the catalysts at operating conditions Six catalysts coming either from industrial or pilot reactors were studied The deactivation level (for hydrogenation reaction) call be determined by XPS analysis quantifying the Ni(Co)MoS' mixed phase amount. The spent catalyst active phases characteristics, at different levels of deactivation, firstly evidenced that the coke particularly influences the CoMo active phase (X-ray photoelectron spectroscopy) lowering the 'CoMoS' mixed phase amount. On the spent NiMo catalysts. most of the nickel is segregated (XPS, Extended X-ray Absorption Fine Structure, Transmission Electronic Microscopy/Energy Dispersive Spectroscopy) even after low residence time in the unit (pilot plant origin) In both cases it leads to the progressive deactivation of the catalyst The coke does not seem to influence the 'NiMoS' mixed phase amount excepted at its life-end. (C) 2009 Elsevier B.V. All rights reserved