Atmospheric residue desulfurization (ARDS) process is extensively used in upgrading of heavy petroleum oils and residues to more valuable clean environmentally friendly transportation fuels and to partially convert the residues to produce low-sulfur fuel oil and hydrotreated feedstocks. Graded catalyst systems in multiple reactors are used in the process in order to achieve hydrodesulfurization (HDS), hydrodemetallization (HDM), hydrodenitrogenation (HDN), and conversion of residues to distillates at desired levels. The characteristics of the feedstocks processed in different reactors are significantly different. The quality of the feed entering the second reactor is strongly dependent on the operating severity in the first reactor and can have an important impact on the performance of the catalysts in the following reactor with regard to various conversions and deactivation rate. In the present work, a systematic study was conducted on the effect of two industrial catalyst types, namely, MoO3/Al2O3 ( HDM) and Ni/MoO3/Al2O3 (HDS) catalysts, in the range of 360-420 degrees C operating temperature on product quality in hydrotreating straight run Kuwait atmospheric residue. The liquid products and their asphaltene fractions from different runs were characterized by various techniques including C-13 NMR and elemental analysis, and the effect of catalyst and operating severity on product quality was assessed. Special attention was paid to the changes in the characteristics of asphaltenes as a function of operating temperature and catalyst type. The results revealed that, besides the usual heteroatoms removal reactions, such as HDS, HDM, and HDN, asphaltenes and resins in the residual oil feed were converted to saturates and aromatics during the hydrotreating process. The aromatic rings in the asphaltenes remaining in the product oil become more condensed and less alkyl-substituted with increasing operating severity disregarding the types of catalyst used. The aromaticity and degree of condensation in the product asphaltenes were higher for the HDM than for the HDS catalyst. The catalyst's hydrogenation activity appears to play a dominant role in determining the nature of the asphaltenes in the product oil. Since the quality of the liquid products, particularly the quality of the residual asphaltenes in the product oil from different catalyst beds, plays a key role in catalyst deactivation and fuel oil stability, the results are considered to be very valuable for optimization of the operating conditions as well as on catalyst selection for hydroprocessing of residual oil in an ARDS process.