The joint valorization of high-density polyethylene (HDPE) and light cycle oil (LCO) has been studied via hydroprocessing with the aim of valorizing the HDPE and reducing the sulfur and polyaromatic contents in the LCO. Experiments have been carried out in a batch type reactor under the following conditions: 320-400 degrees C; 80 bar; feed: catalyst mass ratio, 20:1; LCO:HDPE mass ratio, 10:1. CoMo/Al catalyst showed higher LCO hydrodesulfurization activity than the other tested catalysts (NiMo/SiAl and NiW/HY), reaching a hydrodesulfurization conversion of 99.3 wt% (72 ppm of sulfur in the liquid product) at 400 degrees C. Furthermore, a moderate dearomatization was obtained, reaching a polyaromatic conversion of 76 wt%. In the hydroprocessing of LCO and HDPE mixture, the joint feeding lightly increases hydrodesulfurization conversion and has no significant impact on product distribution, with HDPE conversion being 31 wt%. These results are promising for valorizing waste plastics by incorporating into a first LCO hydroprocessing stage. The hydrodesulfurizated liquid product should be treated in a second hydrocracking stage using a noble metal catalyst supported on strong acid functions.