Abstract: The changes of the content and structure of four fractions in the vacuum residue of Saudi Arabia light crude oil (ALVR) pre- and post hydrotreating were investigated in an autoclave at different reaction temperatures. The results showed that after the hydrotreating, the saturate content is increased greatly, while the aromatic and resin contents are decreased in the hydrotreated residue; the contents of four fractions changes regularly with the increase of the reaction temperature. The H/C mol ratio and molecular weight of four fractions in the hydrotreated residue are decreased while the fraction of aromatic carbons (f_a) is increased after the hydrotreating. With the increase of reaction temperature, the H/C mol ratio, molecular weight and the fraction of paraffin carbons (f_p) of four fractions are decreased, while f_a and the content of resin and asphaltene are increased in the hydrotreated residue; meanwhile, the total rings and aromatic rings of resin and asphaltene are decreased. The four fractions in the residue have undergone hydrogenolysis and hydrodealkylation during the hydrotreating. Bridge bonds between the units of resin and asphaltene may break by hydrotreating, leading a decrease of the unit number of resin and asphaltene, which is more prominent at higher reaction temperature.