The nature and composition of the coke deposited on Pt–Pd catalysts supported on acid carriers during the hydroprocessing (hydrocracking and hydrotreating) of light-cycle oil (LCO) has been studied. Five types of supports have been used: a commercial cracking catalyst, alumina, Hβ zeolite, and two HY zeolites (with different acidities). The hydrocracking runs have been performed at 350 °C and 50 bar for up to 24 h. The characterization of the deactivating species on the catalyst used has been performed using temperature-programmed oxidation (TPO) coupled with mass spectrometry (MS) and Fourier transformed infrared (FTIR) spectroscopy, ultraviolet–visible (UV–vis) spectroscopy, and comprehensive two-dimensional gas chromatography/mass spectrometry (GC × GC/MS) analysis of the soluble coke extracted from the deactivated catalyst. The complex composition of the coke has been simplified in three families, each related to a different composition and location. The composition of the coke (and the amount of each type of coke) strongly depends upon the catalyst properties, particularly the features of the support: acidity and micropore topology.