Abstract: The removal of sulfur and changes of sulfur forms in Oman vacuum residue by hydrotreating were investigated on a pilot plant. The results illustrated that the content of total sulfur in hydrotreated residue reduced gradually with the hydrotreating. Over 80% of total sulfur in the residue can be removed at three temperatures (T-5℃, T℃, T+5℃), although a higher temperature can enhance the desulfurization effect. The residue fractions of aromatic, resin, asphaltene and saturate contain about 60%, 32%, 8% and 1% of total sulfur, respectively; however, the sulfur content in each fraction is in the order of asphaltene>resin>aromatic>saturate. The sulfidic sulfur content in the residue fraction decreased and the thiophenic sulfur content increased with the heaviness of residue fraction. Sulfur forms exhibit influence on the hydrodesulfurization effect; the removal of sulfidic sulfur is much easier than that of thiophenic sulfur. The residue fractions are also different in the desulphurization effect, depending on their molecular size and structure; the sulfur removal ratio of saturate and aromatic is higher than that of resin and asphaltene.