The flammability and thermal decomposition kinetics of recycled polyethylene terephthalate (RPET)/recycled polypropylene (RPP) blends filled with CaCO3 were investigated. The thermal decomposition kinetics were determined by using various models such as the Flynn-Wall-Ozawa, Kissinger, and Kim-Park, which would define the thermal stability of the blends through the determination of their decomposition activation energies. Meanwhile, the flammability of the materials was also determined through the limiting oxygen index (LOI) method. It was found that blends with higher RPP content or contain CaCO3 exhibited higher resistance to thermal degradation judging from their higher activation energies. Furthermore, it was found that the isoconversion kinetic of the Flynn-Wall-Ozawa model could provide a better estimation of the decomposition activation energy at each stage of degradation. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013