An integrated adsorption process for deep desulfurization of diesel fuel was proposed and examined. Conventionally hydrodesulfurized straight run gas oil (HDS-SRGO) having less than 50 ppm sulfur was also adsorptively treated with activated carbon fiber (ACF) to attain the ultra low sulfur gas oil having less than 10 ppm sulfur. The ACF, used in cleaning-up HDS-SRGO, was successively examined in straight run gas oil (SRGO) treatment to enhance its hydrodesulfurization (HDS) reactivity over conventional CoMo catalyst by removing the nitrogen and refractory sulfur species contained in SRGO. Such integrated adsorption-reaction process makes it possible to utilize the maximum adsorption capacity of ACF and achieve ultra deep desulfurization og SRGO. Regeneration of used ACF with a conventional solvent was proved very effective in restoring its adsorption capacity. (c) 2004 Elsevier Ltd. All rights reserved.