Plastic wastes accumulation increased each year in the environment. Plastics types are different such as polystyrene (PS), polyethylene terephthalate (PET), polypropylene (PP), low-density polyethylene (LDPE), high-density polyethylene (HDPE) and polyvinyl chloride (PVC). In this paper, catalytic pyrolysis of Polystyrene and Polyethy terephthalate were studied to find the effect of PET on the pyrolysis of PS. The reaction took place in stainless batch tubular reactor to determine the effect of temperature and residence time. The maximum liquid products yield at optimum temperature and heating time(60 min) was 77% , 67.56%, 54% and 37.48% for PS, 10%PET + PS, 20%PET + PS and 30%PET + PS respectively. The liquid produced were characterized by GC-MS at optimum condition. The component of the liquid are styrene monemer, toluene, alpha-methylstyrene, 1,3 Diphenylpropane, 1-Phenylnaphthalene, 4-phenyl-1 butene. Styrene monomer was found to be the main product in the pyrolysis of PS, 10%PET+PS, 20%PET+PS and 30%PET+PS.The physical properties such as density, viscosity, and caloric value of the produced liquid was investigated ,the results was 0.9 g/cm3 ,2-3 Cp, and 40-45 MJ/kg respectively.