The degradation of polystyrene in various Lewis acids [aluminum chloride, ferric chloride, borontriflouride etherate, and tin(IV) chloride] at different temperatures (75-125 degreesC) has been studied in this work. The evolution of the molecular weight distribution (MWD) has been modeled using continuous distribution kinetics with a stoichiometric kernel for random chain scission. The degradation rate was the highest in the presence of aluminum chloride. The reactions were also carried out at different aluminum chloride concentrations, and the degradation rate was proportional to the fourth power of the Lewis acid concentration. The activation energy of polystyrene degradation in the presence of aluminum chloride, determined from the temperature dependence of the degradation rate coefficient, was 7.7 kcal/mol.