Secondary recycling is an alternative to solve at least part of the worldwide pollution problem caused by persistence of petrochemical plastic materials in the environment. In this work we report the secondary recycling of disposable polystyrene (PS) using cassava starch (Manihot esculenta Crantz) and a natural plasticizer extracted from a palm tree of the Amazon: Buriti (Mauritia flexuosa L.) oil. C-13-NMR spectroscopy reveals incorporation of the oil in the polymer matrix. Although phase separation had occurred, SEM depicts a very good dispersion of the thermoplastic starch (TPS) in the PS matrix with distinct domains. Thermal analyses indicate smaller thermal stability of the PS/TPS blends compared to PS and that possess intermediate characteristics between the pure PS and TPS, confirmed by DRX. Kinetic study shows a lowering of the activation energy for the thermal degradation of the blends.