Co-refining process of biomass and vacuum gas oil (VGO) with hydro-donor (tetralin or aromatic enriched fraction of fluid catalytic cracking slurry (FCCRF)) was explored at 320 degrees C for 20 min in this work. FCCRF exhibited a much higher capacity for hydrogen donation in accelerating the co-refining process than tetralin. After introducing FCCRF, the maximum yields of co-refining oil and gases (89.51 wt.% and 5.43 wt.%, respectively), along with the minimum char yield (5.06 wt.%) were obtained. The products were analyzed via gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS) and elemental analysis. The results showed that the hydro-donor helped to produce more oxygen-containing compounds (OCCs). The produced OCCs in co-refining oil successfully reduced the viscosity of oil by 60-70%. A co-refining mechanism of VGO and sawdust (represented by hemicellulose) was proposed to explain the co-refining behavior and hydro-donor effect. The elemental equilibrium analysis and Van Krevelen diagram illustrated the industrial feasibility of the sawdust-VGO co-refining process with a hydro-donor. (C) 2017 Elsevier Ltd. All rights reserved.