Aqueous-phase processing (APP) shows a lot of potential for the effective utilization of bio-oil. Water extraction, low-temperature hydrogenation of the water-soluble portion of bio-oil, and reforming (to H-2) or dehydration/hydrogenation (to C-1-C-6 alkanes) are the three constituent steps of APP. In this work, two compounds representing the bio-oil aqueous fraction, viz., xylenol and maltol, were selected. Hydrogenation of these compounds in the aqueous phase was investigated in the 318-348 K range in a slurry reactor using a Ru/C catalyst. Kinetic data for the reactions with xylenol and maltol were collected in the chemical control regime and modeled using LangmuirHinshelwood kinetics. The dependency of the initial reaction rates upon H2 partial pressure in the 0.69-2.07 MPa range was linear. The surface reaction between the chemisorbed reactants, viz., atomic hydrogen and substrate, was considered as rate-determining.