Idemitsu Kosan Co., Ltd. had developed the iron (Fe) containing zeolite catalysts for the fixed bed residual oil (resid) hydrodesulfurization (HDS) unit. The catalysts, named R-HYC, showed high resid hydrocracking (HYC) activity by increasing the middle distillates and concurrently decreasing the bottom fuel oil. Commercial application with resid HDS units had been realized in 1980s-1990s. Because of relatively less HDS activity of R-HYC, the catalyst has been replaced with commercial HDS catalysts to correspond the lowering sulphur regulation in recent years. In order to meet the present demands on refineries, such as coping with the soaring oil price and shrinking market for fuel oil as the primary energy sources, we resumed developing new R-HYC catalysts, which should have good abilities in both HYC and HDS. For more practical purpose to be applicable to the existing atmospheric residue desulfurization (ARDS) unit, a suitable combination for the R-HYC catalyst with the conventional hydrotreating catalysts, such as hydrodemetallization (HDM) and HDS, has been under investigation. (C) 2010 Elsevier B.V. All rights reserved.