In recent years, the increasing demand of diesel fuel has led the scientific community and the industry to investigate new technologies and feedstocks for diesel production. Light Cycle Oil (LCO) could be an interesting substitute for diesel fuel as it presents a similar boiling range to diesel. LCO upgrading can be achieved via catalytic hydroprocessing, a refinery-based technology, enabling heteroatom (sulfur, nitrogen, metals) removal and saturation of olefins and aromatics. LCO hydrotreatment took place in the hydroprocessing unit at the Chemical Process & Energy Resources Institute of the Centre for Research and Technology Hellas and was used as a base case, and then the co-hydroprocessing of LCO with Waste Cooking Oil (WCO) was investigated as a means to improve the properties of LCO while improving the end fuel carbon foot-print. The results showed that there are some inhibitory properties like heavy sulfur species, which are difficult to be removed via hydroprocessing. For this reason, the fractionation of LCO up to 350 °C was performed with the objective of isolating these heavy sulfur species and some other polyaromatic compounds that are difficult to be removed. The light fraction of LCO (LCO_cut) was led for hydroprocessing and then was also mixed with WCO and co-hydroprocessed. In this study, all these four experimental hydroprocessing cases are developed in an Aspen simulation model of a hydrotreating process using experimental process data in order to evaluate how the distillation and the WCO addition affect the LCO hydrotreatment process. The results have shown that the combination of LCO distillation and WCO addition renders high quality compatible hybrid products, presenting the most favourable environmental profile, as compared to the other examined cases. In particular, the case of co-hydroprocessing of LCO_cut with WCO addition presents the lowest environmental impacts, leading to a reduction of about 2-12 % of GHG emissions, rendering this pathway more sustainable and attractive for the refinery industry.