A kinetic study of the pyrolysis of oil shale mixed with LDPE was carried out by thermogravimetric analysis (TGA). Different runs were performed at heating rates between 2 and 50 K min -1 . The results obtained from this comprehensive investigation indicated that they are three main degradation steps and the increase in the heating rate caused a lateral shift in the thermograms. The difference of weight loss ( w) between experimental and theoretical, calculated as algebraic sums of the mixture for different heating rates of 2, 10, 20 and 50 K min -1 , is about 8-11% at 670-840 K. These experimental results indicate a significant synergistic effect during pyrolysis of oil shale mixed with LDPE. Kissinger-Akahira-Sunose method, Friedman's method, Flynn-Wall-Ozawa method and Coats-Redfern have been used to determine the activation energies of materials degradation. The analyses of the processes mechanism of materials by Criado et al. method and Coats-Redfern method showed: the most probable model for the pyrolysis process of oil shale kerogen agrees with diffusion model (D4 mechanism); and the thermal degradation process of LDPE goes to a mechanism involving "Contracting cylinder" model (R2 mechanism), whereas the mixture degrades following a kinetic model of D4.