A process is disclosed for converting a particulate solid biomass material to a high quality bio-oil in high yield. The process comprises a pretreatment step and a pyrolysis step. The pretreatment comprises a step of at least partially demineralizing the solid biomass, and improving the accessibility of the solid biomass by opening the texture of the particles of the solid biomass. In a preferred embodiment the liquid pyrolysis product is separated into the bio-oil and an aqueous phase, and the aqueous phase is used as a solvent in the demineralization step and/or in the step of improving the accessibility of the solid biomass by opening the texture of the particles of the solid biomass.