Pyrolysis of olive residue, polystyrene and their mixture (1:1 weight ratio) were investigated by thermogravimetry. Experiments were conducted under N2 atmosphere at four heating rate of 2, 10, 20, and 50 K/min from room temperature to 900 K. The results showed that the thermal degradation temperature range of olive residue was 430-660 K, while that of polystyrene was 580-800 K. In general, we can note that the domains of degradation are well differentiated. Discrepancies between the experimental and calculated TG/DTG profiles were considered as a measurement of the extent of interactions occurring on co-pyrolysis. The maximum degradation temperatures of polystyrene in the mixture were higher than the polystyrene pure. The calculated residue was found to be higher than experimental. These experimental results indicate a significant synergistic effect during pyrolysis of mixture of olive residue and polystyrene at the high temperature region. The kinetic studies were performed using the Friedman kinetic-modeling equation. The overall activation energies were: 165 and 219 kJ/mole for hemicellulose and cellulose, respectively; 180 kJ/mole for polystyrene; and 160, 215, and 166 kJ/mole for hemicellulose, cellulose, and polystyrene in the mixture, respectively. Thus, it has been found that there exists an overall synergy, when two materials were pyrolyzed together.