The evolution of asphaltenes has been studied under hydroconversion conditions with an ebullated bed on a Buzurgan ( Middle Eastern) feedstock. A bench unit was used to produce effluents in residue conversion conditions in the range of 55- 85 wt %. Under those conditions, asphaltene conversion was observed in the range of 62- 89 wt %. Asphaltenes from the feedstock and unconverted asphaltenes were then characterized using size exclusion chromatography ( to evaluate asphaltene size) and 13C nuclear magnetic resonance ( to evaluate the evolution of the average molecular structure parameters of asphaltenes). The work clearly shows that ( i) the asphaltene unit size decreases when conversion increases and ( ii) the aromaticity of asphaltenes increases due to dealkylation.