A process for the refining of crude oil, comprising a separation unit of the crude oil, consisting of at least one atmospheric distillation unit for separating the various fractions, a unit for the conversion of the heavy fractions obtained, a unit for improving the quality of some of the fractions obtained by actions on the chemical composition of their constituents, and units for the removal of undesired components, characterized in that the heaviest fraction, the atmospheric distillation residue, is sent to the conversion unit comprising a hydroconversion reactor in slurry phase or of the ebullated bed type, into which hydrogen or a mixture of hydrogen and 3/4 S is introduced in the presence of a suitable nanodispersed hydrogenation catalyst.