The detailed composition description of poly(ethylene terephthalate) (PET) pyrolysis products still remains a challenge due to the complexity of the obtained mixture. In this context, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analyses by negative ion electrospray ionization (−) ESI and positive ion laser desorption ionization (+) LDI were performed for characterizing waxy products and solid residues, respectively. (−) ESI FT-ICR MS revealed that the DBE of waxy compounds ranges from 5 to 20 and the carbon number from 7 to 30. Terephthalic acid was the dominant peak in the low m/z range, and 1,4-benzenedicarboxylic acid, 1,2-ethanediyl ester was evidence at higher m/z value. Based on the oxygen atom number, the waxy products displayed seven class compounds. The most significant contributions were observed for O4 and O8 species. van Krevelen plots revealed that the most abundant aromatic species followed a monotonous behavior (alignment according to a straight line), highlighting the presence of homologous series. The analysis of the solid residue by (+) LDI FT-ICR MS showed that three classes of compounds were observed: oxygenated compounds, carbonaceous materials, and hydrocarbons. As the temperature increased, the solid residue tended to be associated to a homogeneous structure consisting of fullerene clusters Cn (with n ranging from 30 to 96 at 410 °C and from 50 to 106 at 480 °C). C60 was systematically the most abundant fullerene.