The thermal decomposition behavior and kinetics of dicyclopentadiene petroleum resin (DPR) and hydrogenated dicyclopentadiene petroleum resin (HDPR) were extensively explored. Both resins had two complex overlapping pyrolysis stages. The activation energy of DPR pyrolysis varied between 79−236 kJ mol⁻¹. The pyrolysis of DPR mainly contained depolymerization accompanied by repolymerization. The main product was cyclopentadiene. By contrast, the initial pyrolysis rate of HDPR was relatively slow. The activation energy of HDPR pyrolysis ranged from 67−217 kJ mol⁻¹. The pyrolysis process of HDPR is mainly ring opening and dehydrogenation reaction. Alkenes, alkynes and hydrogen were its main products. These results indicate DPR was easy to decompose and part of the molecule was changed to cross-linked reticular structure by the repolymerization at high temperature environment. Compared with that, HDPR has lower thermal mass loss rate and higher thermal structure stability.