Disclosed is a combination process for improved hydrotreating and catalytic cracking of hydrocarbon oils, including: contacting residual oil, catalytic cracking cycle oil, and optional distillate oil with a hydrotreating catalyst under hydrotreating conditions in the presence of hydrogen followed by separation of the reaction products to obtain hydrogenated tail oil and other products; contacting the hydrogenated tail oil and optional normal catalytic cracking feedstock oil with a cracking catalyst under catalytic cracking conditions followed by separation of the reaction products; wherein the hydrogenated tail oil and/or normal catalytic cracking feedstock oil are separated into at least two fractions prior to contacting the hydrogenated tail oil and/or normal catalytic cracking feedstock oil with the cracking catalyst.