The accumulation of industrial plastic waste in the environment is a global growing concern. Thermochemical process is a preferred method to dispose plastic waste mainly because it can reduce volume of the waste; however, the thermochemical disposal of plastic waste can emit harmful chemical species such as benzene derivatives and polycyclic hydrocarbons. As an effort to overcome this challenge, supported metal catalysts (carbon-supported Pd and Pt catalysts) were used to inhibit the formation of polycyclic compounds and biphenyl derivatives by pyrolysis of polyethylene terephthalate (PET). Less polycyclic compounds and biphenyl derivatives were generated during the Pd or Pt-catalyzed PET pyrolysis than non-catalytic PET pyrolysis. The concentrations of polycyclic compounds and biphenyl derivatives were 107 % and 56 % lower for the Pt-catalyzed pyrolysis at 700 °C than non-catalytic pyrolysis, respectively. The Pt catalyst was more effective to suppress the generation of polycyclic compounds and biphenyl derivatives during the PET pyrolysis than the Pd catalyst at temperatures from 400 to 800 °C. This was likely because the Pt sites catalyzes decyclization reaction and/or free radical mechanism that is dominant in thermal cracking of carbonaceous substances such as PET. The results of this study would help develop environmentally friendly industrial plastic waste treatment methods via thermochemical processes.