A chemiluminescence study on photo-irradiated isotactic polypropylene in the presence of three new HALS compounds, mercapto-1,3,5-triazinic phenolic stabiliser (antioxidant T) and Tinuvuin 770 as standard was carried out. The oxidation prevention was assessed by the calculation of the main kinetic parameters of thermal degradation process (oxidation induction time and maximum oxidation rate). Supplementary stability tests were performed on i-PP containing four stabiliser couples (triazine + HALS) and the cooperative factors resulting from the synergistic activities of oxidation prevention couple were determined. A kinetic treatment of the chemiluminescence data obtained from thermal ageing of stabilised isotactic polypropylene is presented.