Mo (content ranging from 0 to 18.8 wt%) is used as an additive in Ni-containing sol-gel derived catalysts NiCuMo/SiO2 for the hydrotreatment of guaiacol as a model compound in biomass derived pyrolysis liquids. The catalysts had a high Ni loading, from 39 to 51 wt%, promoted by copper with an atomic ratio Cu/Ni close to 0.12. The experiments were done in autoclave at 320 °C, at a hydrogen pressure of 9 MPa. Addition of molybdenum results in an increase in activity of the catalyst, accompanied with an increase in selectivity towards the deoxygenation reactions. This is attributed to the formation of solid solutions NiMo(Cu) and 4+ and 5+ charge states of Mo on the catalyst surface. Moreover, an increased mean metal particles size is observed at higher Mo loading, due to the weakening of the interaction between the active component (Ni) and the stabilizer (SiO2) in the presence of Mo.