The thermal behavior of plastics (PS and HDPE) and their blends with biomass (bamboo, empty fruit bunch and sawdust) was investigated in this paper. The individual devolatilization behavior of each of the fuels obtained separately was compared with the behavior of the biomass blends with plastics at various blends. The result shows that the thermal decomposition of the materials can be characterized by one single reaction stage while that of the blends can be characterized by two decomposition reaction stages. The results of the analyses suggested that the co-pyrolysis characteristics of the blends are quite different to the combination of the individual materials and therefore the possible synergic effect points to the existence of chemical interactions during co-pyrolysis between the plastic and biomass fractions of the blends. While up to 25% deviation was observed between the experimental and calculated TGA for HDPE/biomass blends, up to 40% was observed for PS/biomass blends. The examination of the kinetic of the blends indicated that an increase in plastic percentage in the blends leads to decrease of activation energy for the first decomposition stage reaction and subsequently increases the activation energy for the second decomposition stage reaction. (c) 2014 Elsevier B.V. All rights reserved.