Abstract The kinetics of the weak chemiluminescence (CL) and peroxyl radical decay after UV irradiation of isotactic polypropylene (PP) have been studied. A correlation has been found between CL and the chain termination reaction in PP post-oxidation at room temperature in air. The kinetics of CL decay, its corrspondence with kinetics of peroxyl radical decay, the relative quantum yield of CL per radical termination and the effects of the plasticizer in accelerating both radical termination and CL decay, have been determined. Kinetic features of CL decay indicates the distributions of peroxyl radicals on both rate constants of termination and quantum yields of CL in the acts of the disproportionation of two peroxyl radicals. In terms of these distributions it is possible to describe quantitatively observed kinetics of CL decay under the post oxidation of PP after the UV irradiation in air.